SCSI vs. ATISCSI SCSI-2, developed to improve
speed and compatibility among different SCSI devices, became a standard in 1991. With a bus width of eight bits and bus speed of 5MHz, total throughput worked out to about 5MB per second.
SCSI-2 was
succeeded by various flavors of the specification. Fast SCSI moved the bus speed up to 10MHz, and Wide SCSI expanded the bus width to 16 bits (in SCSI lingo, "Wide" means a 16-bit bus). Fast Wide
SCSI has a 16-bit wide bus, a bus speed of 10MHz and a peak transfer rate of 20MB a second.
Ultra SCSI, which replaced Fast SCSI, offers a 20MHz, 8-bit bus, enabling a peak transfer rate of 20MB per
second. Ultra2 SCSI raises the bus speed to 40MHz. Ultra2 Wide SCSI, with a 40MHz, 16-bit bus, is capable of 80MB-per-second throughput. Ultra160/m SCSI, also called Fast-80 SCSI or Ultra3 SCSI, maintains
the 40MHz bus speed, but again doubles the throughput to 80MB per second. The Ultra3 Wide SCSI protocol extends the peak transfer rate to 160MB per second. On the horizon is Ultra 320 SCSI, which promises a
peak transfer rate of 320MB a second.
ATA
ATA, which stands for Advanced Technology Attachment, is extremely inexpensive to manufacture, and has become the most common storage interface
on personal computers. Compaq developed ATA in 1985 as a low-cost attachment for hard drives.
In 1986 manufacturers took steps to place the ATA interface and controllers on the PC motherboard,
and the modern implementation of ATA was born.
Around 1994, the original ATA became a bottleneck as drives and PC systems became faster and required more address space. Western Digital developed the
more-ambitious Enhanced IDE (EIDE) interface, which featured numerous enhancements beyond extra speed, such as support for larger drives and added support for ATA Packet Interface (ATAPI). ATAPI is the
standard by which CD-ROMs, tape drives and other packeted transfer devices are attached to the same ATA controllers as hard disks.
Fast ATA and EIDE (minus ATAPI) both contributed to ATA-2, which
became part of the official standard in 1996. ATA-3, introduced in 1997, provided support for even-larger drives. A year later, ATA-4, often called UMDA/33, UMDA or Ultra ATA, boosted transfer speeds to
33.3MB per second and added official ATAPI support. ATA-4 also introduced Direct Memory Access (DMA) and Ultra DMA
ATA-5, also called ATA/66 or UMDA/66, currently ships on most systems, boosting the
peak transfer speed to 66MB per second. It also implements an 80-pin connector and can support drives larger than anything conceivable in the near future. ATA/100 is becoming popular now, as drives and
controllers start to become more popular.
In conclusion, ATA tends to be designed with an eye on the bottom line. SCSI's primary goal is performance. |
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