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742 Chapter <strong>13</strong> Optical Storage<br />
The SCSI bus enables computer users to string a group of devices along a chain from one SCSI host<br />
adapter, avoiding the complication of installing a separate adapter card into the PC bus slots for each<br />
new hardware device, such as a tape unit or additional CD-ROM drive added to the system. These<br />
traits make the SCSI interface preferable for connecting a peripheral such as a CD-ROM to your PC.<br />
Not all SCSI adapters are created equal, however. Although they might share a common command<br />
set, they can implement these commands differently, depending on how the adapter’s manufacturer<br />
designed the hardware. ASPI was created to eliminate these incompatibilities. ASPI was originally<br />
developed by Adaptec, Inc., a leader in the development of SCSI controller cards and adapters who<br />
originally named it the Adaptec SCSI Programming Interface before it became a de facto standard.<br />
ASPI consists of two main parts. The primary part is an ASPI-Manager program, which is a driver that<br />
functions between the operating system and the specific SCSI host adapter. The ASPI-Manager sets up<br />
the ASPI interface to the SCSI bus.<br />
The second part of an ASPI system is the individual ASPI device drivers. For example, you would get<br />
an ASPI driver for your SCSI CD-ROM drive. You can also get ASPI drivers for your other SCSI peripherals,<br />
such as tape drives and scanners. The ASPI driver for the peripheral talks to the ASPI-Manager<br />
for the host adapter. This is what enables the devices to communicate together on the SCSI bus.<br />
The bottom line is that if you are getting a SCSI interface CD-ROM, be sure it includes an ASPI driver<br />
that runs under your particular operating system. Also, be sure that your SCSI host adapter has the<br />
corresponding ASPI-Manager driver as well. There are substantial differences between SCSI adapters<br />
because SCSI can be used for a wide variety of peripherals. Low-cost, SCSI-3–compliant ISA or PCI<br />
adapters can be used for CD-ROM interfacing. In contrast, higher-performance PCI adapters that support<br />
more advanced SCSI standards, such as Wide, Ultra, UltraWide, Ultra2Wide, and so on, can be<br />
used with both CD-ROM drives and other devices, such as CD-R/CD-RW drives, hard drives, scanners,<br />
tape backups, and so forth. To help you choose the appropriate SCSI adapter for both your CD-ROM<br />
drive and any other SCSI-based peripheral you’re considering, visit Adaptec’s Web site.<br />
The SCSI interface offers the most powerful and flexible connection for CD-ROMs and other devices.<br />
It provides better performance, and seven or more drives can be connected to a single host adapter.<br />
The drawback is cost. If you do not need SCSI for other peripherals and intend on connecting only<br />
one CD-ROM drive to the system, you will be spending a lot of money on unused potential. In that<br />
case, an ATAPI interface CD-ROM drive would be a more cost-effective choice.<br />
√√ See “Small Computer System Interface,” p. 514.<br />
ATA/ATAPI<br />
The ATA/ATAPI (AT Attachment/AT Attachment Packet Interface) is an extension of the same ATA (AT<br />
Attachment) interface most computers use to connect to their hard disk drives. ATA is sometimes also<br />
refered to as IDE (Integrated Drive Electronics). ATAPI is an industry-standard ATA ATA/ATAPI is an<br />
extension of the same ATA interface most computers use to connect to their hard disk drives. ATA is<br />
sometimes also refered to as IDE (Integrated Drive Electronics). ATAPI is an industry-standard ATA<br />
interface used for CD/DVD and other drives. ATAPI is a software interface that adapts the SCSI/ASPI<br />
commands to the ATA interface. This enables drive manufacturers to take their high-end CD/DVD<br />
drive products and quickly adapt them to the ATA interface. This also enables the ATA drives to<br />
remain compatible with the MSCDEX (Microsoft CD-ROM Extensions) that provide a software interface<br />
with DOS. With Windows 9x and later, the CD-ROM extensions are contained in the CD file system<br />
(CDFS) VxD (virtual device) driver.<br />
ATA/ATAPI drives are sometimes also called enhanced IDE (EIDE) drives because this is an extension<br />
of the original IDE (technically the ATA) interface. In most cases, an ATA drive connects to the system<br />
via a second ATA interface connector and channel, leaving the primary one for hard disk drives only.
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