Acer PCI to Ultra SCSI RAID Controllers DAC960PG - Manual (Page 80)

G-22 DAC960PG and DAC960PJ Installation Guide
Ultra SCSI (Fast 20 SCSI)
A high performance SCSI protocol that has a bus speed of 20 Megabytes per
second in the Narrow SCSI configuration and 40 MB in the Wide SCSI (Fast
20 Wide SCSI) configuration.
Ultra Wide SCSI
16-bit wide Ultra SCSI (IS devices), double the speed of narrow SCSI.
Ultra2 SCSI (Fast 40 SCSI)
A higher performance SCSI protocol than Ultra SCSI. Ultra2 SCSI has a bus
speed of 40 Megabytes per second in the Narrow SCSI configuration and 80
Megabytes in the Wide SCSI (Wide Ultra2 SCSI) configuration.
Wide SCSI
A SCSI protocol and signal definition providing 16-bit wide data path.
Write-Back Cache
A caching strategy whereby write operations result in a completion signal
being sent to the host operating system as soon as the cache (not the disk
drive) receives the data to be written. The target disk drive will receive the
data at a more appropriate time in order to increase controller performance.
An optional cache battery backup can be used to protect against data loss as
a result of a power failure or system crash.
Write-Through Cache
A caching strategy whereby data is written to the SCSI drive before a
completion status is returned to the host operating system. This caching
strategy is considered more secure, since a power failure will be less likely to
cause loss of data. However, a write through cache results in a slightly lower
performance.