Optical Disk Drives: Technologies Offer Choices for Storage

Article excerpt

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. …