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Optical disk drives: technologies offer choices for storage.

There are three basic categories of optical disc drives--CD-ROM, Write Once Read Many (WORM) and Erasable/Rewritable. CD-ROM drives are definitely the most prevalent in the educational community, a phenomenon spurred on by the proliferation of educational CDROM titles. WORM drives are becoming more visible as administrators begin to understand the possible applications and benefits such drives provide.

Erasable/Rewritable or write many read many drives are also coming into their own and may well overshadow WORM drives. Since an erasable drive can also be used to write once to a disc, it takes WORM applications one step further. The problem here is data security. Erasable media can be written on many times. As a response to this, a new breed of drives has emerged-the multifunction optical disc drive. Multifunction drives perform both tasks by writing to WORM and/or erasable media.

* More and Less

New items utilizing CD-ROM technology have also become available, the first of which is a CDROM changer. The Pioneer DRM-disc 600 changer's magazine holds up to six CD-ROM or CD audio discs, offering over three gigabytes of data storage. in addition, its two SCSI ports support the daisy-chaining of up to seven units from a single host computer.

Network-compatible, the DRM-gives 600 students access to multi-volume CD-ROM databases or acts as a CD-Audio jukebox. Audio connectors enable the unit to be connected to an external sound system; it sports a built-in stereo headphone jack with volume control.

The included JUKE utility program's menu builds a CD library plus offers an on-screen, remote control program window. A second utility supplied, Multi-Play Controller (MPC), is memory resident. MPC lets users access the changer while running other programs.

Suited for use with portable, laptop or desktop computers, the CD Porta-Drive from CD Technology, Inc. displays CD-ROM materials on any portable computer. As an added benefit, the unit can be moved easily due to its compact, lightweight (4 lbs.) design. An external power supply, battery pack and optional carrying case further enhance the unit's portability.

The CD Porta-Drive runs on DOS and Macintosh computers via a SCSI system interface and is network compatible. With a data capacity of 683MB, it also ships with software that enables it to play audio CDs. The unit's base price is $895; an additional amount is charged depending on the platform of intended use.

Dr. H.D. Mayor in the department of microbiology College of Medicine uses the CD Porta-Drive to access DNA sequences and other genetic bank information stored on CD-ROM. The microbiologist has been using her CD-ROM drive with a Macintosh 11 for three months; it is used in the department's anatomy, cell biology and microbiology courses. She also takes advantage of its portability, taking it to various computers on campus. Mayor believes the drive will become even more useful to her as more CD-ROM discs are incorporated into department's curricula.

* Magnetics and Optics

CD-ROM and WORM technology are purely optical. In contrast, erasable/rewritable drives, developed over a year ago, use magneto-optical (MO) technology. The discs for these drives have several layers of polymers-usually either glass or plastic-with the active, center layer being magnetized.

The device's laser heats up the polymer in the center layer. A nearby electromagnet reacts to this process by switching the polarity to either positive or negative. Particles are frozen into position when the polymer cools. The only way data integrity can be lost is through complete destruction of the disc.

The only problem with MO is that it takes a little longer to write data because three passes are used-one to erase the section of the disc that will be written on, one to write the data and one to verify. Speed can be increased by instructing the drive to skip the verify pass. As a result, animation files are often unable to be stored using this technology. Animation files can be read, however, quick and easily.

The standard media format used for erasable drives is 5.25" and has a shelf life of up to 25 years. Most drives comply with ISO and ANSI standards, making formatted discs portable to other manufacturers' devices. MO drives have recording capacities of 130MB, 600MB, 650MB and 1GB (gigabyte). The 1GB format may not conform to industry standards, however, since most use proprietary media that must be purchased from the manufacturer.

The hammerdisk erasable magneto-optical drives from FWB, Inc. contain proprietary installation software to generate low-level SCSI partitions for multiple operating systems such as A/UX. Rated the best overall in the November 1990 issue of MacUser, the hammerdisk 600S, as well as two other models, are compatible with NEXT computers, PS/2s and compatibles, RISC System/6000s, IBM ATs and compatibles and Sun workstations as well as AppleShare networks.

XYXIS Corp.'s Erasable Optical Disc Subsystem supports Macintosh, DOS, Novell, OS/2, Unix, DEC, Amiga and Sun. Its drivers ensure that all files are closed via mount/unmount commands before cartridges are ejected. This feature is necessary for Mac, Sun and Unix platforms.

MacinStor, the erasable optical subsystem for Macintosh computers by Storage Dimensions, is available in 600MB and 1GB sizes. The Eddy Award-winner offers an average seek time of 35ms. Other related products are LaserStor for DOS and OS/2, LANStor for Novell networks and X/Stor for Unix platforms.

Other companies include Corel Systems Corp., who offers the Corel 650, and LaCie Ltd., with their SMO-S501 600MB drive. Peripheral Land inc. (PLI) offers a 600MB magneto-optical drive plus the Optical Disk Library, a jukebox that holds up to 36GB of data stored on 56 removable discs. A smaller model, the Jukebox Jr., holds one optical drive and up to ten cartridges.

* Mini Optical Drives

The newest offering in the erasable/rewritable genre is the advent of mini optical drives. These drives use 3.5" media rather than the standard 5.25". The REO-130 by Pinnacle Micro is a SCSI device with a 28ms access time. Each 3.5" disc holds 128MB of data rather than the standard-sized media's 600MB or 650MB, but can last nearly as long, with a shelf life of 10 years.

The drive is available in both internal and external models with interface kits for Mac, Sun, DEC and DOS computers. One benefit is that the palm-sized media can easily be transported and even mailed. Monetarily, the REO-130 lists for $2,995, a difference of up to $2,000 when compared to standard-sized units. The smaller media is also more affordable.

* When to WORM

As hinted at earlier, WORM drives do have advantages over erasable drives in that they offer complete data security; WORM media cannot be erased. While an MO drive can function in write-once environments, its integrity in that situation is user-dependent. Human intervention, whether intentional or accidental, can cause irreparable damage to days or months worth of data.

In response to this need for a dependable means of archiving data, a new hybrid product has emerged--multifunction drives. In essence they can use ma-neto-optical technology to write to both MO and write-once media. This way the same machine can perform two distinct tasks. For data that will be permanently stored, WORM discs are inserted and used. Other data can be recorded on erasable optical discs.

At this time there are only two multifunction optical disc drive manufacturers-Panasonic Office Automation and Pioneer Electronic Corp. The latter company uses magneto-optical technology in their drives while the former utilizes phase-change technology.

Pioneer's LaserMemory DE-U7001 is billed by the company as "the world's first optical disc drive usable for both rewritable and WORM type media." Pioneer first announced the drive in 1989 and began shipping in 1990.

Standing only 3-1/4" high, the DE-U7001 easily installs into a computer or acts as a stand-alone peripheral subsystem. It conforms to ISO standards and is compatible with other Pioneer 5.25" WORM drives, allowing existing software and databases to continue to be used. Switching between WORM and rewritable configurations is accomplished either by manually flipping a switch on the unit or via a software command from the host computer.

The two media accepted by the unit are: Pioneer's DEC-702 rewritable disc, which utilizes magnetic discs described earlier; and the DC-502A 5.25" WORM optical disc, a dye media that provides reliable long-term storage. Both have a storage capacity of 654MB. This drive can be purchased from Laser Magnetic Storage International.

Panasonic, on the other hand, manufactures the LF-7010, a multifunction drive based on phase-change technology. A disc for this drive contains thin films whose elements exhibit both an amorphous and a crystalline state.

Unlike MO drives, the original condition of the spot that will be written on using phase-change is irrelevant because the two lasers used change the material to either amorphous or crystalline. The 8-mW laser will turn a spot crystalline, while the 18-mW laser will melt the recording material at a higher temperature to return it to the amorphous state.

In effect, phase-change technology directly overwrites previously written data with new data, reducing the write time with its single-pass technology. (Actually, there are two passes, one to write and one to verify, however the verify can be turned off.)

Phase-change optical storage systems accept Panasonic's WORM media, which hold 940MB of data, and phase-change discs, which store 1 gigabyte of data on a single cartridge. These numbers are achieved through the unit's ability to vary the amount of data stored on each disc track.

Corel Systems Corp. plans to sell the drive, bundled with their CorelDRIVER software, under the name KURATA Optical Disc Drive at a retail price of approximately $4,495.

* Many Options

The types of material placed on CD-ROM is expanding, taking advantage of the media's ability to store large amounts of data. For example, many well-known companies-Sierra Online in Course Gold, Calif., and Activision of Menlo Park, Calif., etc.-are putting their computer games on CDROM because the discs can store large graphics and sound files. This technology will have a definite and positive effect on education as its implementation continues to spread.

Obviously there are many options available to administrators and media managers for data storage. After ranking the importance of security versus flexibility, either WORM or erasable drives will emerge as the drive of choice. However if both activities will be performed frequently, perhaps multifunction drives would better fit the bill.

The different types of technology available offer the same administrators even more choices. What is apparent is that there is an optical disc drive designed for every application.
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Title Annotation:New Trends In ...
Author:Greenfield, Elizabeth
Publication:T H E Journal (Technological Horizons In Education)
Date:Mar 1, 1991
Words:1749
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