604 Chapter 20
usually SCSI based so PCs usually have to have an extra expansion card fi tted to provide
this interface (see later). Recordable CDs rely on a laser-based magneto-optical system
to “ burn ” data into the recorded medium. Once written, data cannot be erased. Software
exists (and usually comes bundled with the drive) which enables the drive to be used as a
data medium or an audio carrier (or sometimes as both). There exist a number of different
variations of the standard ISO-9600 CD-ROM. The two most important are the (HFS/
ISO) Hybrid disk, which provides support for CD-ROM on Mac and PC using separate
partitions, and the Mixed mode disk, which allows one track of either HFS (Mac) or ISO-
9600 information and subsequent tracks of audio.
A number of alternative removable media are available and suitable for audio use; some
are based on magnetic storage (like a fl oppy disk or a Winchester hard-drive) and some on
magneto-optical techniques—nearer to CD technology: Bernoulli cartridges are based on
fl oppy disk, magnetic storage technology. Disks up to 150 MByte are available. Access
times are fast; around 20 ms. SyQuest are similar. Modern SyQuest cartridges and drives
are now available in up to 1.3 GByte capacity and 11-ms access times, making SyQuest
the nearest thing to a portable hard drive. Magneto-optical drives use similar technology
to CD, they are written and read using a laser (Sony is a major manufacturer of optical
drives). Sizes up to 1.3 GBytes are available with access times between 20 and 30 ms.
20.6 Hard Drive Interface Standards .............................................................................
There are several interface standards for passing data between a hard disk and a computer.
The most common are the SCSI or Small Computer System Interface, the standard
interface for Apple Macs; the IDE or Integrated Drive Interface, which is not as fast as
SCSI; and the Enhanced IDE interface, which is a new version of the IDE interface that
supports data transfer rates comparable to SCSI.
20.6.1 IDE Drives
The Integrated Drive Electronics interface was designed for mass storage devices, in
which the controller is integrated into the disk or CD-ROM drive. It is thereby a lower
cost alternative to SCSI interfaces in which the interface handling is separate from the
drive electronics. The original IDE interface supports data transfer rates of about 3.3
Mbytes per second and has a limit of 538 Mbytes per device. However, a recent version
of IDE, called enhanced IDE (EIDE) or Fast IDE, supports data transfer rates of about