UltraSCSI technology refers to DIGITAL's invention of cabling, connectors,
and expanders that have become ANSI standard extensions which revolutionize
the physical deployment of SCSI technology. UltraSCSI product implementation
increases the efficiency of new, larger, and more efficient disks and
adapters and essentially doubles the peak performance in SCSI devices.
UltraSCSI components are backwards compatible with SCSI-2 components.
UltraSCSI defines additional speed choices during arbitration/selection to
allow negotiation of higher speeds in addition to wide/narrow and
slow/SCSI-2. UltraSCSI preserves all other SCSI logic, enabling all software
and firmware to remain stable.
UltraSCSI devices operate at 20mhz transfer speeds, achieving a bandwidth of
40MB bits per second on wide buses. All UltraSCSI disks are only offered in
Singled-ended 16-bit wide bus variants.
SCSI type Bus speed Transfer rates
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Bus Clock Rate Transfer Rate
Fast SCSI 10mhz 10MB's on 8-bit (narrow bus)
(Fast-10) 20MB's on 16-bit (wide bus)
UltraSCSI-1 20mhz 40MB's
(Fast-20)
UltraSCSI-II 40mhz 80MB's
UltraSCSI-III 80mhz 160MB's (under development)
UltraSCSI (Fast-20) Advantages
The current UltraSCSI technology is called Fast-20 (20 Mbit/wire and 40
Mbytes/second on a wide bus).
Existing SCSI-2 technology is called Fast-10 (10 Mbit/wire and 20
Mbytes/second).
UltraSCSI (Fast-20) components provide the following advantages:
Double bandwidth
Double throughput
More than double configuration distances
Provide fair arbitration, allowing more systems to share a SCSI
bus
Physically smaller
Cost same or less
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