#
Upgrading & Repairing PCs Eighth Edition

#

# - 18 -

# Tape and Other Mass-Storage Drives

- Tape Backup Drives
  - The Origins of Tape Backup Standards
  - The QIC Standards
  - Common QIC Tape Backup Types
  - Newer High-Capacity QIC-Standard Drives
  - QIC-Tape Compatibility
  - Other High-Capacity Tape Drive Standards
  - Choosing a Tape Backup Drive
  - Tape Drive Installation Issues
  - Tape Drive Backup Software
- Removable Storage Drives
  - Types of Removable Media Drives
  - Magnetic Media Drives
  - Magneto-Optical Drives
  - Comparing Removable Drives
  - Write-Once, Read Many (WORM) Drives
  - Compact Disc Recordable (CD-R) Drives

#

The data backup and archive needs on a personal computer can be overwhelming. People with large hard drives, numerous application programs installed, and those who generate a large amount of data should find it necessary to back up their computers on a weekly or even a daily basis.

In addition, a critical need on today's PCs is data storage space. Sometimes it seems the storage requirements of a PC can never be satisfied. On nearly any PC used for business, study, or even for fun, the amount of software installed can quickly overwhelm even a "jumbo" hard drive. Data used infrequently should be archived to another storage device to save space on the primary storage devices.

This chapter focuses on tape backup drives and removable media disk drives, which increasingly are used to solve the problems of the growing need for data storage space and the need for a fast and efficient way to back up many megabytes of data.

## Tape Backup Drives

Any computer book worth reading warns repeatedly that you should back up your system regularly. Backups are necessary because at any time a major problem, or even some minor ones, can corrupt the important information and the programs stored on your computer's hard drive, rendering this information useless. A wide range of problems can damage the data on your hard drive. Here is a list of some of these data-damaging problems:

- Sudden fluctuations in the electricity that powers your computer (power spikes) resulting in data damage or corruption.
- Overwriting a file by mistake.
- Mistakenly formatting your hard disk when you meant to format a floppy.
- Hard drive failure resulting in loss of data that has not been backed up. Not only do you have to install a new drive but, because you have no backup, you also must reinstall your software programs, disk-by-disk.
- Catastrophic damage to your computer (storm, flood, lightning strike, fire, theft). A single lightning strike near your office or home can destroy the circuitry of your computer, including your hard drive. Theft of your computer, of course, is equally devastating. A recent, complete backup greatly simplifies the process of setting up a replacement computer.
- Loss of valuable data due to a computer-related virus. One single download could contain a virus that can damage valuable files and even your entire hard drive. With several hundred new viruses appearing each month, no anti-virus software program can keep you entirely safe. A recent backup of non-infected, critical files can help repair even the worst damage.

Backups are also the cure for such common headaches as a full hard drive and the need to transfer data between computers. By backing up data you rarely use, then deleting the original data from your hard drive, you free up the space once occupied by that data. If you later need a particular data file, you can retrieve that file from your backup. Sharing large amounts of data between computers--as when you send data from one city to another, for example--is more easily accomplished by backing up the data to a tape and sending the tape.

Regardless of how important regular backups are, many people avoid making them. A major reason for this lapse is that for many people, backing up their system is tedious work when they have to use their floppy disk drive. When you use your floppy drive, you may have to insert and remove hundreds of disks to back up all of the important programs and data, depending on whether your backup software includes data compression, the capability to specially encode backed-up data in less space than it takes to store the same data on your hard drive.

Tape backup drives are the most simple and efficient device for backing up your system. With a tape backup drive installed in your system, you simply insert a tape into the drive, start your backup software, and select the drive and files you want to back up. The backup software copies your selected files onto the tape while you attend to other business. Later, when you need to retrieve some or all of the files on the backup tape, you insert the tape in the drive, start your backup program, and select the files you want to restore. The tape backup drive takes care of the rest of the job.

This section examines the various types of tape backup drives on the market, describing the capacities of different drives as well as the system requirements for installation and use of a tape drive. The following topics are covered in this chapter:

- Common standards for tape backup drives, including QIC-40 and QIC-80 drives
- Common backup tape capacities
- Newer higher-capacity tape drives
- Common tape drive interfaces
- The QIC standards for tape backup drives
- Portable tape drives
- Tape backup software

### The Origins of Tape Backup Standards

The evolution of tape backup standards is similar to that of standards for many computer components. Using tape to back up computer data became a common practice long before accepted tape backup standards existed. At first, reel-to-reel systems (somewhat similar to old reel-to-reel audio tape recorders) were used to store data. The most commonly used tape--quarter-inch--eventually developed into a de facto standard. But each tape system manufacturer used its own data-encoding specifications for backup tapes. Variations included not only the number of tracks and data density on the tape, but also the interface used to connect the drive to the computer.

In 1972, more than a decade before the introduction of the first IBM-PC, the 3M company introduced the first quarter-inch tape cartridge designed for data storage. The cartridge measured 6x4x5/8 inches. Inside this cartridge, the tape was threaded onto two reels. The tape was moved from one reel to another during the recording or read-back process by a drive belt. Because of the reliability of this tape cartridge, the demand for tape backup systems began to grow, despite the lack of established standards for storing data on these cartridges.

The result of this lack of standardization was that quarter-inch tapes written on one manufacturer's tape backup drive generally could not be read on another manufacturer's quarter-inch tape drive. One problem created by this situation was that the way particular manufacturers encoded data on a tape continued to change. If a particular model of tape drive became disabled and the manufacturer had discontinued that particular drive and no longer used its encoding format, the data stored on tapes written on the disabled drive could be unavailable until the drive had been sent for repairs. In the event the manufacturer could not repair the drive, the data was lost forever.

As with other computer components, such as hard drive interface cards, consumers were the force behind standardization. Consumers clamored for standardized tape drives that could read tapes created on different tape drives manufactured by different companies.

### The QIC Standards

In response to this demand for standardization, the tape drive industry formed the Quarter-Inch Cartridge Drive Standards Inc., sometimes simply referred to as the Quarter-Inch Committee (QIC). In 1983-84, the first tape drive based on a QIC standard was shipped: the QIC-02, which stored 60M of data encoded in nine data tracks on roughly 300 feet of tape.

As the technology improved, and because the 4x6x5/8-inch size of the first tape cartridges was difficult to adapt to the 5 1/2-inch drive bays in most IBM-compatible PCs, QIC adopted a second standard for tape cartridges roughly the size of an audio cassette. These mini-cartridges measure roughly 3 1/4x2 1/2x3/5 inches.

These two cartridge sizes are currently used in various QIC-standard tape drives. A two-letter code at the end of the QIC standard number designates whether the tape standard is based on the full-sized cartridge or the mini-cartridge. These two-letter codes are shown in the following:

- DC in a QIC standard number stands for data cartridge, the 4x6x5/8-inch cassette.
- MC in a QIC standard number stands for mini-cartridge, the 3 1/4x2 1/2x3/5-inch cassette.

The new QIC-5B-DC, for example, is a 5G-capacity tape based on the QIC standard for the full-sized cartridge. The new QIC-5010-MC, which has 13G capacity, is based on the mini-cartridge standard.

Table 18.1 shows the common QIC-standard tape formats and their technical specifications.

Unlike software whose version numbers (1.0, 1.1, 2.0, 2.1) tell you which version of the software is the most recent, the QIC number designation does not serve as an accurate guide to understanding which QIC-standard tape drives are the latest technology. The designations QIC-100 and QIC-128, for example, were used for tape drives marketed long before today's QIC-40 and QIC-80 drives. Furthermore, the QIC-standard version numbers frequently have no correlation with the capacity of the tape cassettes or mini-cartridges used with a drive bearing a QIC designation. For example, the QIC-40 tapes have a capacity of 60M; the QIC-80 tapes, a capacity of 120M.

QIC-standard backup tapes are magnetic media, primarily ferric oxide, and are recorded in a manner similar to the way data is encoded on your hard drive, using either modified frequency modulation (MFM) or run-length limited (RLL) technologies.

#### Table 18.1 Specifications of QIC-standard Quarter-inch Tape Cassettes and Minicartridges QIC Minicartridge Tape Standards
DC-2000 QIC Tape Standards (Approximate Dimensions 3 1/4-by-2 1/2-by-3/5)

QIC Standard Number | Capacity (w/o Compression) (1) | Tracks | Data Transfer Rate (Approximate) | Data Density | Tape Length (2) | Encoding Method | Interface Type
QIC-40 | 40MB/60MB | 20 | 2MB-to-8MB | 10,000bpi | 205 ft. | MFM | Floppy or optional
|  |  | minute |  | /307.5 ft. | adapter card |
QIC-80 | 80MB/120MB | 28 | 3MB-to-9MB | 14,700bpi | 205 ft./ | MFM | Floppy or optional
|  |  | minute |  | 307.5 ft. |  | adapter card
QIC-100 | 20MB/40MB | 12 or 24 | -- | 10,000bpi | -- | MFM | SCSI (4) or QIC
(obsolete) |  |  |  |  |  |  |
QIC-128 | 86MB/128MB | 32 | -- | 16,000bpi | -- | MFM | SCSI or QIC
QIC-3010 | 255MB | 40 | 9MB minute | 22,000bpi | 300 ft. | MFM | Floppy or IDE
QIC-3020 | 500MB | 40 | 9MB minute | 42,000bpi | 400 ft. | MFM | Floppy or IDE
QIC-3030 | 555MB | 40 |  | 51,000bpi | 275 ft. | MFM | SCSI-2 or QIC
QIC-3040 | 840MB (3) | 42 or 52 |  | 41,000bpi | 400 ft. | RLL | SCSI-2 or QIC
QIC-3050 | 750MB | 40 |  | -- | 295 ft. | RLL | SCSI-2 or QIC
QIC-3060 | 875MB | 38 |  | -- | 295 ft. | RLL | --
(inactive) |  |  |  |  |  |  |
QIC-3070 | 4GB | 144 |  | 68,000 | 295 ft. | RLL | SCSI-2 or QIC
QIC-3080 | 1.6GB | 50 |  | 60,000 | -- | RLL | SCSI-2 or QIC
QIC-3110 | 2GB | 48 |  | -- | -- | RLL | SCSI-2 or QIC
QIC-5010 | 13GB | 144 |  | -- | -- | RLL | SCSI-2 or QIC
QIC-11 | 45MB | 9 | -- | -- | 450 ft. | MFM | QIC-02
(DC-300) |  |  |  |  |  |  |
QIC-24 | 45MB/60MB | 9 | -- | 8,000 | 450 ft. | MFM | SCSI or QIC-02
|  |  |  |  | 600 ft. |  |
QIC-120 | 125MB | 15 | -- | 10,000 | 600 ft. | MFM | SCSI or QIC-02
QIC-150 | 150MB/250MB | 18 | -- | 10,000bpi | 600 ft. | MFM | SCSI or QIC-02
|  |  |  |  | 1,000 ft. |  |
QIC-525 | 320MB/525MB | 26 | 12MB minute | 16,000bpi | 1,000 ft. | MFM | SCSI or SCSI-2
QIC-1000 | 1GB | 30 | 18MB minute | 36,000bpi | 760 ft. | MFM | SCSI or SCSI-2
QIC-1350 | 1.35GB | 30 | 18MB minute | 51,000bpi | 760 ft. | RLL | SCSI-2
QIC-2100 | 2.1GB | 30 | 18MB minute | 68,000bpi | 875 ft. | RLL | SCSI-2
QIC-2GB | 2.0GB | 42 | 18MB minute | 40,640bpi | 900 ft. | MFM | SCSI-2
QIC-5GB | 5GB | 44 | 18MB minute | 96,000bpi | 1,200 ft. | RLL | SCSI-2
QIC-5010 | 13GB | 144 | 18MB minute | 68,000bpi | -- | RLL | SCSI-2

(1) Tape capacity may vary according to tape length.
(2) Tape lengths may vary by manufacturer.
*Tape capacity may vary according to tape length.
**Tape lengths may vary by manufacturer.
***1GB with drives based on 0.315-inch tape cartridge.
****SCSI: Small Computer Systems Interface.

### Common QIC Tape Backup Types

The most common QIC-standard drives, QIC-40 and QIC-80, are based on mini- cartridges. Millions of drives based on the QIC-40 and QIC-80 standards are currently installed in computer systems. There are several reasons for the success of QIC-40 and QIC-80, not the least of which is that these two standards resulted in the first generation of economically attractive tape drives which stored data in a manner compatible from one manufacturer to another. In other words, QIC-40 and QIC-80 tape drives and tapes are quite affordable, and backups made on one QIC-40 or QIC-80 tape drive can b0e read in a tape drive built by another manufacturer.

In addition, the compact size of the mini-cartridge used for QIC-40 and QIC-80 tapes has resulted in drives made by numerous manufacturers that fit easily into both 5 1/2-inch half-height drive bays and 3 1/2x1-inch drive bays. Portable tape drives that read and write QIC-80 format tapes are quite common, but QIC-40 drives are near extinction. Unlike a drive that is installed in a computer's drive bay, portable drives can be used to back up any number of computers.

Another reason for the success of QIC-40 and QIC-80 tape drives is that the cost of tapes themselves is considerably lower per megabyte than the cost of a stack of floppy disks that can store the same amount of backup data. For example, a name brand QIC-80 tape that can hold 250M of data (with data compression) costs between $14 and $25. The street price of 13 boxes (10 per box) name brand 1.44M 3 1/2-inch floppy disks, which hold roughly the same amount of compressed data, is about $90. The same number of generic, bulk floppy disks, which many people are hesitant to rely upon for backing up important data, costs nearly $50. Of course, the price difference doesn't include the valuable time spent swapping those disks or the relative cost of storing them.

Most of the QIC-80 drives on the market today have one major shortcoming--the use of the floppy drive interface, especially on an older PC, makes the tape drive performance extremely slow. Data transfers occur at roughly the same slow rate as when data is written to a floppy disk. Controllers that support only the Double Density (DD) floppy drives can only write data at 250Kbps, which is fewer than 2M (millions of bytes) per minute. A floppy controller that supports HD (High Density) drives can operate at 300 or 500Kbps, which is up to 3.75M per minute. The latest ED (Extra-high Density) controllers can operate at rates of up to 7.5M per minute, which is quite good (see Table 18.2). Note that these rates are the maximum raw throughput of the controller, and due to overhead you will never achieve these actual figures in practice.

#### Table 18.2 Floppy Controller Raw Data Transfer Rates

Controller Type | DD | HD | HD | ED
Transfer rate in kilobits per second (Kbps) | 250.00 | 300.00 | 500.00 | 1,000.00
Transfer rate in kilobytes per second (K/sec) | 31.25 | 37.50 | 62.50 | 125.00
Transfer rate in megabytes per second (M/sec) | 1.88 | 2.25 | 3.75 | 7.50

Backup tapes, like floppy disks and hard drives, must be formatted before use. And one aspect of using a QIC-80 tape drive that has not been improved is the time it takes to format a tape. Formatting a 125M length QIC-80 tape can take more than three hours. It's almost impossible to find an unformatted tape because of these long format times. The industry has been preformatting tapes since 1994. Other tape formats have the ability to format on-the-fly, which means they don't require preformatted tapes.

Data is stored on QIC-40 and QIC-80 tapes in MFM format, the format used on floppy disks (and older hard drives). Another similarity between formatting a backup tape, floppy disks, or a hard drive is that the formatting process creates a record-keeping system. The record-keeping system used on QIC-40 and QIC-80 tapes is similar to that on a hard drive or floppy disk.

The QIC standard calls for a file allocation table (FAT) that keeps track of where data is stored on the tape and keeps bad sectors from being used for data storage. A QIC-40 tape is divided into 20 tracks, with each track divided into 68 segments of 29 sectors each. Each sector stores 1K (1,024 bytes). This record-keeping system and the error-correcting system that ensures reliably stored backup data use a total of 30 percent or more of each QIC-40 tape.

Despite the slow backup speeds of tape backup drives on some computers and the time it takes to format tapes, the ease of using a backup tape drive makes it easy to understand the popularity of QIC-40 and QIC-80 tape drives. And that popularity has its benefits. Prices of QIC-80 tape drives--the smallest-capacity tape drives anyone should consider--have plunged in recent years. Brand-name QIC-80 tape backup drives often cost less than $150; sometimes you can buy them for as little as $100 by shopping mail order.

QIC-40 Drives

The first tape backup drives to gain wide acceptance were based on the QIC-40 standard, adopted in 1986. Most early QIC-40 tape drives were built to fit a 5 1/2-inch drive bay. The QIC-40-standard drives use an internal power connector and send and receive data through a cable linked to the floppy controller generally. The first QIC-40 tapes, which had a native capacity of 40M (they could hold 40M of data without data compression), were soon followed by QIC-40 tapes capable of holding 60M without data compression.

One disadvantage of the first QIC-40 tape drives was that because a spare connector had to be used on the floppy drive cable, only one floppy drive could be used on a system in which a tape drive was installed. But with the use of a special cable, more recent QIC-40 drives are installed easily on systems with two floppy drives.

Although a major goal of the QIC organization was to achieve compatibility between tape backup systems, a tape created on one brand of tape drive could not necessarily be read in another brand. Manufacturers still clung to their individual arrangements for the physical placement of data on the tape. The goal of compatibility between tape backup systems became more of a reality with the introduction of QIC-80 drives.

QIC-80 Drives

The QIC-80 tape backup drive is the most popular tape backup drive on the market and the minimum any buyer should consider. QIC-80 tape drives generally are built to fit 3 1/2x1-inch bays, although they usually include a frame and faceplate that enable them to be used in a larger 5 1/2-inch bay. Like the QIC-40 drives, QIC-80 tape systems use an internal power connector. The data connection for a QIC-80 tape backup can be the same type of floppy disk controller connection used for QIC-40 drives, or a special high-speed interface installed in an available expansion slot on the motherboard. The use of a high-speed interface card greatly can increase the data transfer rate and decrease the amount of time needed for a backup.

Generally, a tape created on one brand of QIC-80 tape drive can be read and written to by another manufacturer's drive. This improved compatibility is due in large measure to the QIC-80 standard itself, which specifies not only the type of record-keeping system for each tape, but also the logical data structure of the tape. QIC-80-standard drives can read, but not write, QIC-40 tapes.

Portable Tape Drives

The portable tape drive is one of the most popular tape drive configurations because portables can be moved easily from system to system--desktops, laptops, a single system, or multisystem installations. Portable tape drives are particularly useful to people who use laptops (in which an internal tape backup drive will not fit) and those who want to back up a number of systems on a single tape backup drive. Portable tape drives are good also for people who want to use a tape backup drive for their desktop system but whose system has no available drive bay, as is often the case with small profile, or slimline, desktop systems.

Portable tape drives can meet so many needs because these drives are self-contained. The drive itself is contained in a rectangular box. The unit connects to the computer's parallel port and is powered by a transformer that plugs into a common AC socket.

To set up a portable tape drive, you simply plug the transformer cord into the system unit and an AC socket, connect the data cable to the computer's parallel port, and run the backup software. One limitation of portable units is availability of compatible backup software. Although portable tape drive manufacturers include software that operates the drive, some popular third-party backup software cannot be used with portable drives.

The most popular portable tape drives are available in QIC-80 standards. These models can achieve a data transfer rate of 3M to 6M per minute.

### Newer High-Capacity QIC-Standard Drives

Using a QIC-80 tape drive to back up a network server's 4G drive or other large hard drive packed with data can be as frustrating as swapping floppies during a backup on a system with a more common 200M-500M drive. To back up a 4G network server hard drive with a QIC-40 tape drive without using data compression, for example, you need about 64 tapes. With data compression, the number of tapes drops to 32--but making the backup takes longer.

The solution to this tape-swapping problem is to use a larger-capacity tape drive system. QIC has established a number of standards for higher-capacity tape drive systems ranging from 86M to 13G. Generally, these larger-capacity systems pack data more densely on the tape, using as many as 144 tracks to pack 60,000 bits per inch (bpi) or more onto the tape (compared to the QIC-40's 20 tracks and 10,000 bpi). To achieve these higher capacities, QIC-standards call for tape media with a higher coercivity level of 1,300 oersted or more (compared to QIC-40 and QIC-80 tape media, which has a coercivity level of 550 oersted). High-capacity tapes are also longer. QIC-5010 tapes, for example, are 1,200 feet long (compared to QIC-40 and QIC-80 tapes, both of which are roughly 300 feet long).

> NOTE: Just as the higher coercivity level of 1.44M floppy disks enables an HD drive to write more densely packed tracks than is possible with 720K floppy disks, higher-coercivity tape media enables higher densities as well.

Although tape systems based on the mini-cartridge dominate the market for lower- capacity tape drives (the QIC-40 60M and QIC-80 120M systems), high-capacity tape backup systems are based on both mini-cartridge-sized tapes and full-sized data cartridge tapes. For example, the QIC-525 standard, which has a capacity of 525M (without data compression), is based on the full-sized (4x6x5/8) cartridge. The QIC-5010 standard is based on a mini-cartridge (3 1/4x2 1/2x3/5).

### QIC-Tape Compatibility

Although QIC-standard drives are based on the standard mini-cartridge and the full-sized data cartridge, it would be a mistake to assume that tapes based on the same cartridge standard are always compatible. For example, QIC-5010-standard tapes are incompatible with QIC-40 and QIC-80 tape backup systems, although both standards are based on the mini-cartridge. Similarly, QIC-525-standard tapes are incompatible with earlier standards based on the full-sized data cartridge. The lack of compatibility between tapes based on the same sized cartridge is due to differences in tape drive mechanisms, as well as the coercivity differences between tape standards. Table 18.3 shows the compatibility of common QIC-standard backup tapes.

Tape compatibility is an important issue to consider when you choose a tape backup system. For example, as you can see from Table 18.3, the 4G QIC-3070-standard drive can read only its own tapes and those that conform to the QIC-3030 standard. If you have many QIC-80 tapes containing data that you must be able to continue to access, a better choice might be a drive based on the 2G QIC-3010 standard. The QIC-3010 can read QIC-40 and QIC-80 tapes. This chapter's "Choosing a Tape Backup Type" section covers similar issues to be considered when you purchase a new tape backup drive.

#### Table 18.3 QIC-Tape-Standard Compatibility

QIC Mini-Cartridge Standard | Compatibility
QIC-40 | N/A
QIC-80 | QIC-40 (read-only)
QIC-100 | N/A
QIC-128 | QIC-100 (read-only)
QIC-3010 | QIC-40 and QIC-80 (read only)
QIC-3030 | QIC-3010 (read-only)
QIC-3070 | QIC-3030 (read-only)
QIC-24 | N/A
QIC-120 | QIC-24 (read-only)
QIC-150 | QIC-24 and QIC-120 (read-only)
QIC-525 | QIC-24, QIC-120, and QIC-150 (read-only)
QIC-1000 | QIC-120, QIC-150, and QIC-525 (read-only)
QIC-1350 | QIC-525 and QIC-1000 (read-only)
QIC-2G | QIC-120, QIC-150, QIC-525, and QIC-1000 (read-only)
QIC-2100 | QIC-525 and QIC-1000 (read-only)
QIC-5G | QIC-24, QIC-120, QIC-150, QIC-525, and QIC-1000 (read-only)
QIC-5010 | QIC-150, QIC-525, and QIC-1000 (read-only)

### Other High-Capacity Tape Drive Standards

Although ferric oxide QIC-standard tapes continue to be popular, two other types of tape backup systems are becoming increasingly popular for backing up networks and other systems with large amounts of data: 4mm digital audio tape (DAT) and 8mm videotape.

Sony, which introduced DAT tape, licenses DAT tape technologies to other manufacturers, in effect setting the standard for drives and tapes manufactured by those companies. There is only one company, Exabyte, which manufacturers 8mm tape drive assemblies. As a result, you're assured compatibility. Table 18.4 shows the basic specifications of the DAT and 8mm technology tapes.

Helical scan recording is similar in many ways to the way video images are recorded to videotape. As with QIC-standard tape drives, DAT and 8mm tapes move past the recording heads, which are mounted on a drum. These read/write heads rotate at a slight angle to the tape, writing a section of a helix, or spiral. The tape drive mechanism wraps the tape about halfway around the read/write heads, causing the heads to touch the tape at an angle. With helical scan technology, the entire surface of the tape is used to record data, unlike other technologies in which data tracks are separated by areas of unrecorded tape. This use of the entire tape surface enables helical scan backup drives to pack a much greater amount of data on a particular length of tape.

#### Table 18.4 DAT and 8mm Tape Specifications

Tape Standard | Capacity (w/o Compression) | Data Density | Tracks (Approximate) | Tape Length | Recording Technology | Encoding Format | Interface
DAT tape (4mm metal particle) | 2G/4G | 114Mbit | 1,869 | 195 ft./300 ft. | Helical Scan DataDAT | DDS* | SCSI
8mm video tape | 14G | NA | NA | 120m | Helical Scan |  |

*DDS: Digital data storage

The DAT Tape Drive Standard

DAT (Digital Audio Tape) is a tape standard that has primarily been developed and marketed by Hewlett-Packard. HP chairs the DDS (Digital Data Storage) Manufacturers Group and has led the development of the DDS standards.

The technology behind digital audio tape is similar in many ways to the techniques used to record music and encode it on musical compact discs (CDs). Data is not recorded on the tape in the MFM or RLL formats used by QIC-standard drives; rather, bits of data received by the tape drive are assigned numerical values, or digits. Then these digits are translated into a stream of electronic pulses that are placed in the tape. Later, when information is being restored to a computer system from the tape, the DAT tape drive translates these digits back into binary bits that can be stored on the computer.

DAT tapes can store up to 12G of uncompressed data, or about 24G compressed. Two types of data formats--DDS and DataDAT--are used for DAT tapes; however, DDS type drives are by far the most common. DDS drives are available in three types:

- DDS-1 drives store 2G of uncompressed data (4G compressed).
- DDS-2 drives can store 4G of data uncompressed (up to 8G with compression).
- DDS-3 drives have a native 12M capacity, or 24M compressed.

The new DDS-3 drives offer full read and write compatibility with all DDS-2 and DDS-1 drives. DDS-3 offers three times the capacity and double the data-transfer rates of current DDS-2 drives. DDS-3 drives are designed to provide reliable high-performance backup for medium to large networks at a substantially lower price than 8mm or DLT (digital linear tape) products with similar capacities.

The new HP DDS-3 drive (Model C1537A) has a native capacity of 12G with a transfer rate of 1M/sec. The DDS-3 drive typically can store 24G on a single 125m tape at a rate of 2M/sec using built-in hardware data compression. The new HP DDS-3 drive incorporates several innovations, including the use of a Partial Response Maximum Likelihood (PRML) data-channel detection scheme that enables the tape's read head to differentiate between bits of data picked up simultaneously.

A typical DDS-2 drive costs about $750, while DDS-3 drives are right around $1,000. DDS technology has an excellent track record and a reputation for reliability that has made it the technology of choice for workstation, end user, and network backup.

The 8mm Tape Drive

A single manufacturer, Exabyte, offers tape backup drives that take advantage of 8mm videotape cartridges. These drives are offered in several capacities--1.5G (3G with hardware data compression), 5G (10G with hardware compression), 7G (14G with hardware compression), and 20G (40G with hardware compression)

Although these drives use 8mm videotapes, video technology is not used in the process of recording computer data to these drives. Rather, Exabyte developed its own technology for encoding data on the tapes. The helical scan method is used to record data to the tape.

The 6M/sec data throughput rate of the Exabyte 8mm tape backup drive, compared with the 10M per minute throughput of the DAT drive, makes the 8mm tape drive a more attractive choice. The extraordinary speed and huge capacity of these 8mm tape drives makes them extremely attractive for backing up network servers and for backing up workstations from the server.

DLT (Digital Linear Tape)

Over the last year, a new tape technology has taken off because of its capability to provide high-capacity, high-speed, and highly reliable backup. Digital Linear Tape (DLT) is now considered one of the hottest products in the high-end tape-backup market. DLT started as a proprietary technology belonging to Digital Equipment Corporation. The technology has been on the market since 1991, but in December 1994, Quantum purchased Digital's DLT and magneto-resistive drive technology.

DLT has a capacity of up to 35-70G compressed, and a data-transfer rate of 5-10M/sec or more. This is approximately the same speed as a high speed 8mm drive; however, 8mm has a slight performance advantage in real-world tests.

DLT segments the tape into parallel horizontal tracks and records data by streaming the tape across a single stationary head at 100-150 inches/sec during read/write operations. This is a dramatic contrast to traditional helical-scan technology, in which the data is recorded in diagonal stripes with a rotating drum head while a much slower tape motor draws the media past the recording head.

The result is a very durable drive and a robust medium. DLT drive heads have a minimum life expectancy of 15,000 hours under worst-case temperature and humidity conditions, and the tapes have a life expectancy of 500,000 passes. DLT drives are designed primarily for network server backup, and cost $6,000 to $8,000 or more depending on capacity. With automatic tape changers, DLT drives can be left unattended for many network backup tasks.

Travan Cartridge Tape

3M has created an entirely new tape cartridge standard based on the QIC format called Travan. Tape drives based on Travan technology have had a significant impact on the tape market for PCs and workstations, and drives based on this technology should dominate this market over the next several years.

The Travan platform features a unique drive/mini-cartridge interface that is patented by 3M. The Travan platform fits in a 3 1/2-inch form factor, making it easy to install in a variety of systems and enclosures. Travan drives can accept current QIC and Travan mini-cartridges--a critical need for users, given the installed base of more than 200 million QIC-compatible mini-cartridges worldwide.

Travan cartridges contain 750 feet of .315-inch wide tape. There are currently several different levels of Travan cartridges and drives available called TR-1 through TR-4, each based on a particular QIC standard:

- The TR-1 mini-cartridge provides users with 400M of uncompressed storage, more than doubling the capacity of the industry's top-selling QIC-80 mini-cartridge (125M).
- The TR-2 mini-cartridge, a new modified QIC-3010 drive/cartridge, stores 800M of uncompressed data, which is significantly more than the 340M available in QIC-3010 form.
- The capacity of the TR-3 mini-cartridge, a new modified 3020 drive/cartridge, is 1.6G of uncompressed data (up from 670M in QIC-3020 form).
- The newest Travan cartridge, TR-4, stores 4G of uncompressed data! The Travan migration path for the new drive and mini-cartridge products should exceed 15G of uncompressed storage capacity by 1997, according to 3M.

Notice that virtually all Travan drives offer 2:1 data compression, which doubles the uncompressed native capacity. This means that a Travan TR-4 drive can store up to 8G on a single cartridge! A typical TR-4 based drive, such as those from Hewlett-Packard's Colorado Memory Systems Division, sell for under $400. Because Travan tapes sell in the $40 price range and are available through any of 3M's worldwide network of distributors and resellers, the low cost and high availability of these drives and cartridges make Travan one of the best backup solutions possible for most individuals.

The TR-1 through TR-3 drives usually interface to the system via the floppy controller or parallel port. I recommend using an EPP or ECP parallel port for ease of use and performance. The higher end TR-4 drives often use a SCSI-2 interface, which offers greater performance than either floppy or parallel port interfaces. A typical TR-4 system such as the HP T4000 drive operates at 514K/sec, which is approximately four times faster than floppy-interface systems, providing backup speeds up to 31M per minute native and up to 62M per minute with 2:1 data compression. Using a typical Pentium system, users can back up a 1G hard drive in about 30 minutes. If you are using the floppy controller or parallel port, you can expect backup times about four times longer or about two hours for a 1G drive.

Storage industry leaders such as 3M, HP/Colorado, Iomega, Conner Peripherals, Exabyte, Tandberg Data, AIWA, Pertec Memories, TEAC, Rexon, and Sony offer Travan drives and support future development of Travan drive and recording formats.

### Choosing a Tape Backup Drive

Choosing a tape backup drive can be a simple job if you need to back up a single stand-alone system with a 500M (or smaller) hard drive. The decision becomes more complex if the system has a larger hard drive, or if you must back up not only a desktop system but also a laptop. Choosing a backup tape drive type can be an even more complex program if you must back up a network server's 4G hard drive and perhaps even back up the workstations from the server. As you ponder which backup tape drive type you should choose, consider the following factors:

- The amount of data you must back up
- The data throughput you need
- The tape standard that is best for your needs
- The cost of the drive and tapes
- The capabilities and compatibility of the included driver and backup software

By balancing the considerations of price, capacity, throughput, compatibility, and tape standard, you can find a tape drive that best meets your needs.

> NOTE: When purchasing a tape backup drive, take the time to look through magazines where dealers or distributors advertise. Several publications specialize in PCs and carry advertising from many hardware and software distributors. I recommend publications such as the Computer Reseller News, Computer Hotline, The Processor, and Computer Shopper. These publications cater to people or companies willing to go around the middlemen and buy direct. By reading such publications, you can get an excellent idea of the drives available and the price you can expect to pay.

> While reading about drive capabilities and prices, don't neglect to read reviews of the software included with each drive. Verify that the software capabilities match your expectations and needs. This is especially important if you intend to use the drive on a non-Windows 95 system, because most backup software is tailored for Windows 95 systems.

Capacity

The first rule for choosing a tape backup drive is to buy a drive whose capacity is large enough for your needs, now and for the foreseeable future. The ideal is to buy a drive with enough capacity that you can start your backup software, insert a blank tape in the drive, walk away from the system (or go about other work), and find the backup completed when you return. You can safely store the tape and resume working.

Given that ideal, an internal QIC-80 drive might be just the ticket if you need to back up a single system with a hard drive of 250M or less. If you need to back up several systems, including laptops, with hard drives of 250M or less, a portable QIC-80 drive might be the solution.

If you must back up a large network server hard drive, relying on a QIC-80 tape drive with its 125M capacity (250M with software data compression) is a bad idea. A better choice would be one of the larger-capacity tape backup drive systems detailed earlier in "Other High-Capacity Tape Drive Standards."

Lately, no matter what the capacity needs for a workstation, I have been recommending either DAT drives or the newer Travan drives. These are simply the most cost-effective, highest-performing drives on the market today. The tapes are preformatted, which saves a lot of time, and can store up to 8G on a single Travan TR-4 tape or 24G on a single DDS-3 DAT tape.

You should always make sure that your tape backup media supports a capacity larger than your largest single drive or partition. This will make automated backups possible because you won't have to change a tape in the middle of a backup. Because the DAT drives normally interface via SCSI, you can use a parallel port SCSI adapter to connect the drive to a system's parallel port as well as an internal SCSI adapter. Of course, the internal adapter will perform better, but a portable DAT drive connected via the parallel port can be used to back up many different systems. The DAT media is also cheaper than any other media.

Tape Standards

The next most important consideration, after adequate capacity, is choosing a drive whose tapes meet a standard that is useful to you. For example, if you must be able to restore backup data using any of a number of different tape backup drives, you should ensure that all these drives can at least read the tapes. For this reason, if you have several systems to work with, you should choose a tape standard that will work in them all.

There is no quick, simple answer as to which standard is the best. Many people stick with QIC-standard drives because QIC created the first standards and continues to develop new standards for large-capacity tape backups. But if you need a large-capacity backup tape system, DAT or 8mm may be the correct choice.

If you need backward compatibility with tapes or tape drives you already have, you will need to buy drives that are the same standard or a higher compatible standard. For example, if you need a large-capacity tape drive that is backwardly compatible with your QIC-80 tapes, you should consider the 2G-capacity QIC-3010, which reads QIC-40 and QIC-80 tapes. If, on the other hand, you don't have to worry about data already stored on old tapes, the important considerations may be capacity and performance. Therefore, DAT or 8mm drives may be the best choice.

> TIP: It is important that you make a choice you can live with. If you manage a large installation of computers, mixing QIC, Travan, DAT, and 8mm drives among systems is seldom a good idea.

Software Compatibility

Equally important to your consideration is the software required to operate each drive. Currently, most drives come with software that runs under the Windows 95 operating system. However, finding software that runs equally well under Windows NT or UNIX might be difficult.

Most operating systems have their own software for backing up data to a tape drive. If you intend to use this software, you should verify that the drive you purchase is supported by each piece of software on each system that you intend to use the drive with.

> NOTE: For more information on tape drive software, see "Tape Drive Backup Software" later in this chapter.

Data Throughput

You should consider the 8mm or DLT drives if performance is more important to you than price or compatibility. These drives offer huge capacity and tremendous data throughput--as high as 6M/sec. Large-capacity drives based on newer QIC-standards are capable of 18M per minute throughput. DAT tape drives offer throughput of 10M per minute.

The low end of the tape backup drive performance spectrum is older QIC-80 standard drives. When linked to a floppy controller, these drives achieve 3M to 4M per minute throughput. Even with a dedicated interface card purchased at added cost, QIC-80 drives are lucky to achieve their advertised throughput of 9M per minute. Portable QIC-80 drives are advertised at 3M to 8M per minute, but 2M or 3M a minute is a more realistic figure.

The Cost of the Drive and Tapes

The price of tape drives varies considerably based upon where you buy, so it pays to shop enthusiastically for price after you have settled on the type of drive you want to buy.

The cost of backup tapes also varies widely, depending on where you buy. The same name-brand 12G DAT tape that costs as much as $14 from one vendor can cost $12 from another. The cost of a formatted name-brand QIC-80 (120M) tape can range from $15 to $26, depending on where you buy it. Because many computer retailers and direct channel vendors offer lower prices when you buy three or more tapes at a time, it pays to shop for price and buy the largest quantity of tapes you expect to need.

> TIP: One point worth remembering when you evaluate whether to buy a tape drive is that the cost of the tapes and drive, taken as a whole, is nowhere near as high as the costs (in terms of frustration and lost productivity) of a single data-damaging hard drive problem. Considering that most people are more likely to back up their system if they have a tape drive installed than if they must use floppy disks for the backup, the cost of a drive and tapes is quite small, even on a stand-alone PC used mostly for fun.

### Tape Drive Installation Issues

Each of the tape drive standards covered in this chapter provides a range of options for installation. These options include both internal and external installation. Whether to choose an internal or external drive, and which external drive to choose if that appears to be the best choice for you, is not always a cut-and-dried issue. If you must back up a single computer with a relatively small hard drive (500M or less), an internal QIC-80 drive might be your best choice. If you have to back up several computers with 500M hard drives, or if you must be able to share data between several computers, you might be able to make do with a QIC-80 portable. If your backup needs are not that simple, however, here are some additional considerations:

- If your computer has a large hard drive and you back up often, or if you administer a large number of systems and want to minimize the amount of work you must do and the number of tapes you have to store for each computer, installing large-capacity QIC, DAT, or 8mm tape drives in each computer might be what you need to do.
- If your best choice is a large capacity QIC, DAT, or 8mm tape drive and almost all the computers you administer have an available drive bay, you might choose a portable DAT or 8mm tape system, which can be moved from system-to-system.

> CAUTION: Steer away from nonstandard tape backup drives. For example, some drives may not conform to QIC, DAT, or Exabyte standards. Because Exabyte is the only manufacturer of 8mm tape backup drives, you can be confident that tapes made on this manufacturer's drives can be read on their drives. I would avoid drives based on VHS videotape, for example, because these types of drives are not a true standard and are not very well-supported.

The following sections cover some important installation issues for internally- and externally-mounted drives.

Internal Installation

Virtually all internal tape backup drives available today are designed to be installed in a half-height drive bay. Many are designed to be installed in either half-height drive bays or the smaller drive bays generally used for 3 1/2-inch floppy drives. Drives that can be installed in 3 1/2-inch floppy drive bays generally are shipped in a cage, or frame, that enables them to be installed in a 5 1/4-inch bay. To install the drive in a 3 1/2-inch bay, you remove the cage and the 5 1/4-inch bay faceplate. Most tape drives are between about 5 and 9 inches deep; they require approximately 5-9 inches of clearance inside the system case. To mount tape drives inside the system, use the same rails or cage apparatus used for floppy drives, hard drives, and devices such as CD-ROM drives.

> NOTE: Remember that the drive bay you select needs to have access to the outside of the machine!

> NOTE: Half-height drive bays measure roughly 1.7 inches high by 5.9 inches wide. The smaller drive bays measure 1x4 inches.

Internal tape drives require a spare power connector, usually the larger connector used for hard drives, although some may require the smaller power connector common to 3 1/2-inch floppy drives. If a power connector is not available inside your system, you can buy a power splitter from a computer store or cable supply vendor. A power splitter looks like the letter Y and acts like an extension cord. You unplug the power connector from a device (such as a floppy drive) that's already installed. Then plug the bottom point of the Y into that power connector. The two arms of the Y then provide you with two power connectors.

> NOTE: More information about power connections for drives is available in Chapter 17, "CD-ROM Drives."

Internal tape drives also require an interface to the system. QIC-40 and QIC-80 drives most often connect to the system through the floppy controller. On a system with only one floppy drive, you connect the tape drive to an unused connector on the floppy disk data cable. On systems with two floppy disk drives, you use a special cable linked to the floppy disk data cable--in effect, a splitter cable.

Internal drives other than QIC-40s and QIC-80s usually require a special adapter card, or they may link to a card already installed in your system. This card is usually one of the following: a QIC-standard adapter card, a Small Computer Systems Interface (SCSI) adapter, a SCSI-2 adapter card, or an Integrated Drive Electronics (IDE) card. When purchasing a drive, you must determine which interface you need; make sure that the drive kit includes the adapter card you need or that you purchase the correct card.

External Installation

If you want to move an external tape drive from computer to computer, you must install an adapter card in each system on which you want to use the tape drive. Portable tape backup drives such as the DAT portables have a SCSI-to-parallel port converter that uses the computer's parallel port connector. Adapter cards designed for use with external tape drives have a different connector, depending on the interface used, that is accessible from the back panel of the system unit. These cards are generally QIC-standard, SCSI, SCSI-2, or IDE.

When you buy an external tape backup drive that requires an adapter, you must ensure either that the drive includes the necessary adapter card or that you purchase the card at the same time you purchase the drive. In addition, if you plan to use the external tape drive to back up a number of systems, you must buy a card for each system on which you plan to use the drive.

Power is supplied to external units by a transformer that plugs into an ordinary 120v AC wall socket. Generally, the transformer connects to the external tape drive with a small connector. When you choose an external tape drive, be sure you have enough AC power sockets available for your computer, its peripherals, and the tape drive.

### Tape Drive Backup Software

The most important decision you can make after you choose the tape standard and capacity of your backup tape drive is the backup software you will use with it. Most tape drives are shipped with backup software that generally is adequate for your basic backup needs.

Often, however, third-party software compatible with the drive you have chosen gives you greater flexibility and functionality. For example, some tape drives may be shipped with only DOS-based software. If you want to use one of these drives from within Windows, or on a system running OS/2 or UNIX, you may need to purchase third-party backup software. And if you will be backing up network workstations from a server, you must make sure that the drive is shipped with software capable of performing this function; otherwise, you will need to acquire third-party software.

One important issue with backup software is data compression, special programming that stores data on the backup tape in less space than is needed on the original source disk that is provided with most backup software. Some companies produce backup software that is well-known for especially efficient data compression. In other words, backup software produced by these companies does a better job of compressing large data files into a small amount of space.

> NOTE: The backup software built into Windows 95 supports a variety of QIC 40, 80, and 3010 tape drives that are connected via the floppy controller card, as well as the Colorado Memory Systems QIC 40, 80, and 3010 drives attached via the parallel port. Unfortunately, the Windows 95 backup does not support the majority of tape drives currently on the market! For example, SCSI tape drives of any kind are not supported, and neither are the newer QIC-type drives such as 3020 or Travan. Fortunately, many superior backup programs are available from aftermarket sources. Most of the time, you will get this software with the drive itself. Check with your tape drive manufacturer to verify Windows 95 support.

You may want to take the time to read reviews on backup software in one of the many monthly computer magazines, such as PC Magazine, Windows Magazine, or BYTE Magazine. The reviews can help you determine which backup software does the best job of compressing data; they also provide information on how quickly backup software programs perform a typical backup. The speed of the backup software and its data-compression capabilities are important considerations. Also of great importance is whether the software is easy to use. If your backup software makes backing up more difficult than it has to be, chances are you won't back up as often as you should.

> TIP: Some of the more recent software for tape drives include a "Disaster Recovery" feature. This feature creates a boot disk (floppy) that can be used to quickly reformat a drive and install a basic Windows 95 platform for use with the drive. Look for this feature when considering your purchase decision.

Bundled Software

Before you buy a backup tape drive, you should always check whether the drive includes software that will meet your needs and, if it doesn't, be sure to buy third-party software that does the job. Generally, the software bundled with most tape backup drives will do the job for you--provided that you don't plan to place great demands on the tape drive.

The software included with a QIC-80 drive, for example, generally cannot be used to back up network workstations from the server. If you want to use a QIC-80 drive for this task, you may need to buy special software compatible with your network and the tape backup drive. If you use Windows, Windows NT, OS/2, or UNIX, your backup software must be compatible with your operating system as well as the drive, and you must determine whether the software shipped with the drive will do the job for you.

Third-Party Software

A large number of companies manufacture backup software designed for different types of tape drives and different uses. For example, many manufacturers design their backup software to be compatible with most networks. Others specialize in DOS and Windows backup software. Some specialize in OS/2 software. Others are well-known among those whose computers run in UNIX. You may need to ask a trusted retailer or call the software company itself to determine whether a particular type of software is compatible not only with the tape drive you have chosen, but also with your network and operating environment.

Often, third-party software is easier to use than the software designed by a tape manufacturer. The tape manufacturer's software may have an unfamiliar interface or its commands may seem cryptic to you, even if you have used backup software for years. It is not uncommon for tape manufacturers to include inadequate or even incomplete documentation for the backup software included with the drive, although this is generally the case only with lower-cost models. In such a case, you may be able to solve the problem by purchasing third-party software.

Third-party software often does a better job of data compression than the software designed by a tape manufacturer. In addition, third-party software often includes capabilities not included with the software bundled with many drives. Some of the capabilities you might want to look for include the following:

- Unattended backup scheduling. Enables you to schedule a backup for a time when you won't need to use your computer.
- Macro capability. Use when selecting options and the files to back up.
- A quick tape-erase capability. Use when erasing the entire contents of a tape.
- Partial tape-erase capability. Use when erasing only part of a tape.
- Tape unerase capability. Use when recovering erased data.
- Password-protect capability. Enables you to protect backup data from access by unauthorized persons.

You can find backup software manufacturers by reading some of the many monthly computer magazines, paying particular attention to their usability reviews. Generally, if a backup software product gets good reviews, works on a system configuration such as yours, and has the features you need, it is worth the price you pay.

## Removable Storage Drives

The reason for the shortage of storage space on today's PCs is easy enough to understand. Just take a look at the sheer number and size of the files stored in the two main directories used by Windows (usually C:\WINDOWS and C:\WINDOWS\SYSTEM). The amount of disk space used by the files in those two directories alone can quickly balloon to 80M or more after you also install a few Windows applications. The reason is simple: Nearly all Windows applications place files in one of the Windows directories that the application will use later. These files include those with extensions such as DLL, 386, VBX, DRV, TTF, and many others. Similarly, Windows NT, OS/2, and UNIX, as well as the software applications that run in these operating systems, can require enormous amounts of storage space.

The remainder of this chapter focuses on some of the more advanced data storage options on the market: removable media large-capacity storage drives. Some removable media drives use media as small as a 3 1/2-inch floppy disk, while others use media about the size of a 5 1/4-inch floppy.

These drives, whose capacities range from 35M to 1G or more, offer fairly speedy performance, the capability to store data or less frequently used programs on a removable disk, and the capability to easily transport huge data files--Computer Aided Drawing (CAD) files and graphics files, for example--from one computer to another. Or, you can use a removable media disk to remove sensitive data from your office so that you can lock it safely away from prying eyes.

> NOTE: Removable media drives can also be used to back up critical data from a hard drive. However, the higher price of the media itself (disks or cartridges) makes this use somewhat prohibitive.

> TIP: There are literally dozens of removable storage devices currently on the market. Be sure to compare your chosen solution against the competition before making a final purchase. Be especially wary of missing statistics in press releases and product packaging--manufacturers are apt to omit a specification if their drive doesn't measure up to the competition.

> See Table 18.5 for a direct comparison of the most popular removable drive technologies.

### Types of Removable Media Drives

There are two commonly used types of removable media drives: magnetic media and optical media, also called magneto-optical media. Magnetic media drives use much the same technology used on a floppy disk or hard drive to encode data for storage. Magneto-optical media drives encode information on disk by using newer technology, which is a combination of traditional magnetic and laser technologies.

Magnetic media drives are considerably faster than magneto-optical drives and offer similar capacities. The Syquest magnetic media drives, for example, offer 14ms average access times, compared to the 30ms (or slower) access times of magneto-optical drives. Magneto-optical drives can be more than twice as expensive as magnetic media drives. If you have a great deal of data to store, however, the comparative cost of using a magneto-optical drive drops because magneto-optical media cartridges are considerably less expensive than magnetic media. For example, 10 270M Syquest cartridges can cost roughly $80 each, and 150M Bernoulli cartridges can cost about $90 apiece. The 128M magneto-optical cartridges can cost as little as $25 apiece.

There are also several connection options for the leading removable drives. Although SCSI has been, and continues to be, a popular solution, many drives today connect to the computer's parallel port. This option allows one drive to be easily shared between several different computers. Of course, internal SCSI and IDE solutions remain just as popular for the single machine installation.

> NOTE: Connection or installation of removable media drives is very similar to connecting and installing other internal and external peripherals.

> The installation of external parallel port drives is generally straightforward, requiring a special cable that comes with the drive and installation of special software drivers. See the instructions that come with each drive for the specifics of its installation.

The following sections provide information on magnetic media and magneto-optical drive types.

### Magnetic Media Drives

A small group of companies dominate the market for magnetic removable media drives. One company, Iomega, always tops the list because it developed the first popular large-capacity removable magnetic media drives, and because its disk cartridges are known as the most rugged in the industry. Two other leading names in removable magnetic media drives are Syquest and 3M.

Removable magnetic media drives are usually floppy or hard disk based. For example, the popular Zip drive is merely a 3 1/2-inch version of the original Bernoulli drive made by Iomega. The new 3M LS-120 drive stores 120M on a disk that looks exactly like a 1.44M floppy!

Both the Bernoulli and Syquest designs are their own de facto standard. Other manufacturers market drives based on the Bernoulli and Syquest designs (and some actually manufactured by Bernoulli or Syquest). For example, the Jaz drive from Iomega uses a hard disk cartridge similar to the Syquest. Generally these manufacturers' drives are somewhat less expensive than the Bernoulli and Syquest models. If you are considering one of these compatible drives, however, make sure that the drive you are buying has the same performance characteristics (average access speed, and so on) as the original, and that the drive manufacturer offers the same warranty as the original (Bernoulli, three years; Syquest/SyDOS, two years).

Bernoulli Removable Media Drives

The disk used in the Bernoulli drive is roughly the same size as a 5 1/4-inch floppy disk, although a large shutter, similar to the shutter on a 3 1/2-inch floppy disk, easily differentiates Bernoulli disks from floppy disks. Modern Bernoulli cartridges are available in 35M, 65M, 105M, and 150M capacities. The Iomega Bernoulli MultiDisk 150 drive, the company's newest model, reads and writes all of these drive capacities. In addition, the MultiDisk reads and writes to older Bernoulli 90M disks and reads older 40M disks. The MultiDisk is available in both internal and external models.

Bernoulli disks are widely known as the most durable of the removable media drive types. It is probably safer to mail a Bernoulli cartridge than another type of removable disk because the media is well-protected inside the cartridge. Bernoulli encases a magnetic-media-covered flexible disk (in effect, a floppy disk) in a rigid cartridge in the same way the thin disk of a 1.44M floppy is encased in a rigid plastic shell.

When it rotates in the drive, the disk is pulled by air pressure towards the drive heads. Many people do not think that there is head-to-disk contact in a Bernoulli drive, but indeed there is. As the disk spins, the airflow generated by the disk movement encounters what is called a Bernoulli plate, a stationary plate designed to control the air flow so that the disk is pulled toward the read/write head. At full speed, the head does touch the disk, which causes wear. Bernoulli drives have built-in random seek functions that prevent any single track on the disk from wearing excessively during periods of inactivity. Bernoulli disk cartridges should be replaced periodically because they can wear out. The disk itself spins at speeds approaching the 3,600 rpm of relatively slow hard drives. The drive has an average seek time of 18ms, not a great deal slower than today's medium-priced hard drives.

The Bernoulli MultiDisk 150 drive is available in an internal model, which requires a half-height drive bay, and an external model. The internal model connects to the IDE hard drive adapter already installed in your system. The external model requires a SCSI adapter card with an external connector. The external model is powered by a transformer that connects to a grounded AC wall plug.

Another form of Bernoulli drive from Iomega is the popular Zip drive. This device is available as a external or internal SCSI unit and is also available as an external parallel port device. The drive is capable of storing up to 100M of data on a small removable magnetic cartridge that resembles a 3 1/2-inch floppy disk, and has approximately a 29ms access time and a 1M/sec transfer rate when used with a SCSI connection. If the parallel connection is used, the drive's speed is often limited by the speed of the parallel port.

The Zip drives use a proprietary 3 1/2-inch disk made by Iomega. It is about twice as thick as a standard 3 1/2-inch floppy disk. The Zip drives do not accept standard 1.44M or 720K floppy disks, making this an unlikely candidate for a floppy drive replacement. Zip drives have become popular in use as an external drive for exchanging data between systems, but the major PC manufacturers have not recognized the proprietary format directly in the system BIOS or in the operating system. The popularity and functionality of the Zip drive has now been greatly exceeded by the new LS-120 "floptical" drive introduced by 3M and Matsushita, and supported by Compaq and other major PC manufacturers. More information about the revolutionary LS-120 drive follows in the next few sections.

Removable Media Hard Disk Drives

Syquest manufactures some drives that use 5 1/4-inch cartridges and others that use 3 1/2-inch cartridges. But the Syquest disks, like the Bernoulli cartridges, are easily differentiated from floppy disks. The 5 1/4-inch 44M and 88M cartridges used in some SyDOS drives are encased in clear plastic, as are the SyDOS 3 1/2-inch 105M and Syquest 270M cartridges. The disk spins inside the cartridge at several thousand rpm. Syquest claims a 14ms average access time for the drives it manufactures.

The disks for the Syquest and SyDOS drives are composed of a rigid platter inside a plastic cartridge but are not as well-protected as the disk in a Bernoulli cartridge. Some people consider these disks fragile. If the Syquest and SyDOS cartridges are not severely jostled or dropped, however, they can be transported safely. These cartridges must be carefully protected when they are mailed or shipped.

The Syquest/SyDOS drives are available in internal and external models. The internal models require a connection to the existing IDE hard drive interface card. The external models require a SCSI interface card with an external connector and are powered by a transformer that connects to a grounded AC wall plug.

Another type of removable hard disk drive is the Jaz drive from Iomega. This is physically and functionally identical to the Syquest drives in that it is a true removable cartridge hard disk, except the capacity of the cartridge has been increased to 1G. Unfortunately, the cartridges themselves cost about $100, which is about seven times the cost of a DAT (Digital Audio Tape) cartridge that stores four to eight times more data! The high cost of the media makes the Jaz drive unsuitable for backup compared to traditional tape media, but possibly useful as an add-on external SCSI hard disk.

### Magneto-Optical Drives

Magneto-optical drives, which are manufactured by a large number of companies, use an ingenious combination of magnetic and laser technology to pack data on 5 1/4-inch and 3 1/2-inch disks contained in cartridges. The media itself and the construction of the platter are similar in ways to the media of a CD-ROM disc. An aluminum base is covered with clear plastic, then a layer of magnetic, optically active media particles--an alloy of cobalt, iron, and terbium. A clear plastic coating seals the disk, rendering it nearly impervious to shock, contamination, and damage.

Although the magneto-optical disks are similar to CD-ROM discs, there is a world of difference in the way data is stored. When manufacturers write CD-ROM discs, the laser actually burns pits into the media to represent the data. These pits are read by the laser and translated into the form of computer data. In the case of magneto-optical disks, the magnetically/optically active media is not burned or pitted. Instead, during the writing process a magneto-optical drive focuses a laser beam onto a very tight track--a much thinner track than could be used to store data on a purely magnetic media platter. The laser beam heats the track, and a weak magnetic signal is applied. The result is that only the thin track of heated media receives the magnetic signal and stores the data it contains.

Unlike a CD-ROM disc, a magneto-optical disk theoretically can be rewritten an infinite number of times because the media is never burned or pitted. When the time comes to erase data from or rewrite the disk, the disk is simply reheated with the laser and the old data is removed magnetically so that new data can be recorded. When the magneto-optical drive reads the disk, the drive functions optically--that is, the laser reads the data from the disk (without heating the media).

Because of the thin tracks on which data is written to magneto-optical disks, the data is packed extremely densely: Large amounts of data can be packed on a platter about the same size as common 3 1/2-inch and 5 1/4-inch floppy disks. The current maximum capacity of the 3 1/2-inch cartridges is 230M; the 5 1/2-inch cartridges can hold as much as 1G of data. It is important to note, however, that capacity ratings of magneto-optical disks can be misleading. Magneto-optical disks are double-sided, like floppy disks, but magneto-optical drives have only one read/write head. Therefore, to read or write to the second side, you must manually flip over the cartridge. So only half the disk capacity is available at any one time.

For many applications, magneto-optical drives are tediously slow, although some drives--using refinements of the basic magneto-optical technology--offer data-access speeds that are inching more closely to those of removable magnetic media drives. One reason that magneto-optical drives are slow is that they typically spin the disk at roughly 2,000 rpm--much slower than the 3,600 rpm of a relatively slow hard drive. Another reason for the slow speeds is that the read/write head mechanism, although optically and magnetically advanced, is mechanically a kludge. The massive mechanism of a magneto-optical drive's read/write heads takes much longer to move and settle than the read/write heads of a hard drive or even a removable magnetic media drive.

Magneto-optical drives typically are rated with average access speeds of about 30ms. However, these average access speed figures do not tell the entire story. The process of rewriting a disk can take nearly twice the time it takes to read the disk. Because of the way magneto-optical technology works, all the bias magnetic field of the area of the disk to be written must be oriented in a single direction during the write process. Because of this limitation, during the write process most magneto-optical drives must make a first pass over the disk to align the tracks of the disk that are to be rewritten. Then the drive makes a second pass over the disk to realign, or change the alignment of, the necessary areas. This alignment/realignment process is known as two-pass recording.

New magneto-optical technologies are emerging which use single pass recording of disks. If speed is an important factor in choosing a magneto-optical drive, you should be prepared to pay extra for a drive whose performance is not penalized by two-pass recording technology. In addition, several manufacturers are offering drives that spin the platter at speeds approaching the 3,600 rpm speeds of a hard drive. The performance boost offered by these drives is considerable, but this technology also boosts considerably the prices of these drives.

Most manufacturers adhere to the International Standards Organization (ISO) specifications for magneto-optical disks and drives. The ISO standard calls for all drives to use a SCSI host adapter to interface with the computer. Under the ISO standard, 5 1/4-inch drives must be able to read two different disk formats: disks with 512-byte sectors and disks with 1,024-byte sectors. The disks with 512-byte sectors have a capacity of roughly 600M; those 1,024-byte sectors hold 650M of data. Under the ISO standard, the 3 1/2-inch drives, which are quite popular among first-time purchasers, are required to read only the 128M disks.

Some manufacturers, in addition to designing their drives to meet ISO standards, also design their drives to use a proprietary data format that can increase the capacity of 5 1/4-inch disks to about 1.3G. Both 5 1/4-inch and 3 1/2-inch drives are available as internal and external units.

### Comparing Removable Drives

Deciding on a removable drive is getting tougher with more than a dozen removable drives currently on the market. Iomega and Syquest lead the pack, but new entries from Exabyte and Avatar Peripherals provide their own proprietary drives as well.

Table 18.5 shows a direct comparison between the most popular removable drives on the market.

#### Table 18.5 Removable Drive Specifications

Drive Type | Drive Cost | Disk/Cartridge Cost | Disk/Cartridge Capacity | Average Seek Time | Data Transfer Rate
Iomega Zip Parallel | $149 | $15 | 100M | 29ms | 1.4M/sec
Iomega Zip SCSI | $149 | $15 | 100M | 29ms | 1.4M/sec
Imation LS-120 Internal | $179 | $18 | 120M | 70ms | 4.0M/sec
Syquest 235 Parallel | $250 | $30 | 235M | 13.5ms | 1.25M/sec
Avatar Shark 250 Parallel | $299 | $30 | 250M | 12ms | 1.2 M/sec
Avatar Shark PCMCIA | $299 | $30 | 250M | 12ms | 2.0M/sec
Syquest 235 SCSI/IDE | $299 | $30 | 235M | 13.5ms | 2.4M/sec
Iomega Jaz (SCSI) | $399 | $99 | 1G | 12ms | 5.4M/sec
Avatar Shark iSeries IDE | $30 | 250M | 12ms | 2.5M/sec |
Syquest Syjet SCSI | $399 | $99 | 1.5G | 12ms | 5.3M/sec
Syquest Syjet IDE | $399 | $99 | 1.5G | 12ms | 5.3M/sec
CD-R Drives | $500-$1,000 | $5 | 650M | <150ms | 150K/sec-2.4M/sec

When shopping for a removable drive, keep the following in mind:

- Price per megabyte of storage. Take the cost of the drive's cartridge or disk and divide it by the storage capacity to see how much you are paying per megabyte of storage. This difference in price will become quite apparent as you buy more cartridges or disks for the drive. (Don't forget to factor in the cost of the drive itself!)
- Access time versus need of access. The access and data transfer speeds are only important if you need to access the data frequently or quickly. If your primary use is archiving data, a slower drive may be fine. However, if you plan on running programs off of the drive, choose a faster drive instead.
- Compatibility and portability. Opt for an external SCSI or parallel port solution if you will need to move the drive between various computers. Also verify that the drive has drivers available for each type of machine you want to connect the drive to.

### Write-Once, Read Many (WORM) Drives

The removable media drive known as write-once, read many (WORM) is designed to serve as a nearly bulletproof data archival system. If you have extremely important data files that absolutely must remain in an unaltered state--perhaps accounting or database data--a WORM drive can provide the kind of security you are looking for. Data written to a WORM disk cannot be changed.

The WORM disk is encased in a high-impact cartridge with a sliding shutter similar to the shutter on a 3 1/2-inch floppy disk. The cartridge and the extremely durable nature of the disk inside make WORM disks worry free for data exchange. A WORM drive cartridge is very difficult to damage. The disk itself, with the media sandwiched in plastic, is not unlike a CD-ROM disc or a magneto-optical disk. The technology used to write a WORM disk, however, is more like the technology used for CD-ROM recording than that used for writing to magneto-optical disks. The WORM drive uses a laser to burn microscopic patches of darkness into the light-colored media.

A number of companies manufacture WORM drives but follow no single standard. Therefore, a WORM disk written on one manufacturer's drive is quite unlikely to be readable on another manufacturer's drive. Each manufacturer (sometimes small groups of manufacturers) uses its own proprietary data format and disk capacity, and many use a cartridge size only their drives can handle. For example, most WORM drives are designed for 5 1/4-inch cartridges but some WORM drives handle only 12-inch disks. In addition, although most WORM drives interface the computer via SCSI host adapter, others use different interfaces, some of them proprietary.

Certainly, at least in part because of these incompatibility problems, WORM drives are not big sellers. No more than several thousand are sold each year at prices soaring to the heights--some 5 1/4-inch drives cost several thousand dollars. The 5 1/4-inch-drive cartridges, which range in capacity from 650M to 1.3G, can cost more than $180.

The term niche market is used occasionally to describe a computer product or peripheral that lacks broad appeal or usefulness. Because of its cost and incompatibility problems, WORM drive technology is a niche market product. Unless you must be able to store massive amounts of data and ensure it can never be altered, you are better off buying a magneto-optical drive, or perhaps even a tape backup drive.

### Compact Disc Recordable (CD-R) Drives

Note that a variation on WORM technology is also found in CD-R (CD-Recordable) drives. CD-R drives are indeed WORM; however, they use a special recordable CD-ROM disc that, once recorded, can be played back or read in any standard CD-ROM drive. CD-R drives are very useful for creating master CDs, which can be duplicated for distribution within a company.

CD-ROMs, as you will remember from Chapter 17, "CD-ROM Drives," work by reading the light reflected by a laser striking the surface of the disc. Light is either returned from the disc, or not. CD-R recorders work by using a laser to etch a pattern into the raw media, leaving places where light is reflected or not reflected.

> NOTE: Because of the technical changes in the way the media is made, there can be some problems reading CDs made by CD-R devices in a standard CD-ROM player. Most of these problems just result in poor play performance as the CD-ROM tries to align itself to the CD. However, some very old CD-ROM players can't handle CD-R media.

CD-R Drive History

CD-R drives were originally used to pre-master CDs prior to production of massive quantities by a CD manufacturing facility. The CD-R drive was used to create a few (normally less than 20) CDs that would then be tested to make sure that the program worked or was installed correctly. Then three of the CDs would be sent to the manufacturing facility to be mastered and printed into thousands of CDs.

Writing a CD with a CD-R Drive

CD-R drives generally come in slower speeds than their CD-ROM reader counterparts. The fastest CD-R drives write at 4x normal speed--given the system performance to do so. However, some can read at up to 6x normal speed.

Whenever a CD-R is writing data, it is making one long spiral on the CD, alternating on and off to etch the pattern into the raw media. Because the CD-R can't realign itself like a hard drive, once you start writing, you must keep writing until you're finished with the track, or you will ruin the CD.

You'll recall from Chapter 17 that the normal speed for a CD is 150K/sec. When writing at a 4x speed, the computer must provide data to the CD-R drive at 600K/sec. If the computer isn't able to maintain that data rate, you'll receive a `Buffer under-run` message.

The `Buffer under-run` message indicates that the CD-R had to abort recording because it ran out of data in its buffer to write to the CD. This is the biggest problem that people have with CD-R devices. Providing a fast source to write from--usually a fast SCSI drive--on a system with plenty of RAM will generally help avoid buffer under-run.

CD-R Software

Another difficulty with CD-R devices is that they require special software to write them. Where most removable drives can be used immediately by built-in drives, the CD-R drive must have special CD-ROM burning software.

This software handles the differences between how data is stored on a CD and how it is stored on a hard drive. As you learned in Chapter 17, there are several CD-ROM standards for storing information. The CD-ROM burning software arranges the data into one of these formats so the CD can be read by a CD-ROM reader.

It used to be that CD-ROM burning software required that all of the files on the hard drive be arranged into a single file which was then written to the CD. The single file contained all of the sectors on the CD, which means every file, all of the directory information, plus the volume information. This single file took as much space as the files being placed on the CD. The result was that you had to have about 1.5G of storage to burn a single CD (650M/CD x 2 = 1.3G + overhead~~1.5G).

This is no longer a requirement as most software supports virtual images. The software assembles the directory information and burns it to the CD, then opens each file on the CD and provides the data directly from the original file. This works well, however, because the files are not sequentially located on the hard drive; it must seek track-to-track, which takes longer. As a result, some slower hard drives may not be able to keep up with writing at the maximum 4x rate supported by some drives.

Most software and CD-R drives support a simulate recording mode which performs the same actions as in a normal writing mode; however, the laser isn't powered up to a level to etch the disc. This is useful in testing the performance of your complete system, and if it can't handle the data rate, you don't waste a CD.

CD-R as Mass Storage

CD-R costs are unique when considering a form of mass storage. Most mass-storage mediums enable you to rewrite on the media over and over, and although there is a new breed of CD-R drives called CD-RW which support rewriting a CD, most don't.

Each CD-R CD can be found for less than $5 in quantities of 25 or above. Most other storage mediums have a much greater media cost. Even at deeply discounted pricing, your DAT, 8mm, QIC, or DLT tapes can cost between $20-$100. Removable media costs can range from $75-$300.

Even though tapes store more and their cost per megabyte is much smaller, accessing files on tape can be a time-consuming process. Removable media is generally more expensive and requires that the recipient have the same kind of drive, or the drive must be transported with you when trying to shuttle files from one place to another.

Compared with either tape or other removable media, using a CD-R to burn CDs can be very cost-effective and easy when transporting large files or making archival copies. Another benefit of the CD for making archival copies is that CDs have a much longer shelf life than tapes or removable media.

However, CD-R isn't a very effective backup medium because the CD can only be written once. Because you can't reformat and reuse the CDs, subsequent backups make previous discs disposable at best.

© Copyright, Macmillan Computer Publishing. All rights reserved.