CDB
See Command Descriptor Block
Command Control Block
A software object prepared by the host microcomputer software
for the host adapter to provide it all the control information it
needs to execute a SCSI command. Abbreviated CCB.
Command Descriptor Block
A block of information passed across the SCSI bus to provide the
command, parameter, and address information necessary for the
target to execute the desired functions. Prepared by the host soft-
ware and placed in the CCB to be passed to the target by the host
adapter. Abbreviated CDB.
Common Command Set
A de facto standard SCSI command set for communication with
fixed disk drives. The Common Command Set (CCS) is the basis
for the SCSI-2 command set for all types of peripheral devices.
D
Device Driver
A software program that enables a PC to communicate with
peripheral devices such as fixed disk drives and CD-ROM drives.
Each kind of device requires a different driver. Device driver pro-
grams are stored on a PC’s fixed disk and are loaded into memory
at boot time.
Differential
A term referring to the electrical characteristics of the signals
used on the SCSI bus interface. Differential signals occupy two
conductors with a positive (+) and negative (-) polarity component
of the signal. This minimizes the effect of common mode signal
noise and allows the SCSI bus to operate reliably over greater
distances at a higher speed.
Direct Memory Access
A mechanism that allows hardware control of the transfer of
streams of data to or from the main memory of a computing sys-
tem. The mechanism may require setup by the host software.
After initialization, it automatically sequences the required data
transfer and provides the necessary address information.
Adaptec AHA-2740 Series User’s Manual
Stock Number: 510381-00 / Rev. C (Page G-5)
Print Spec Number: 491709-00 Rev C
Current Date: 9/1/93 ECN Date: 9/14/93
Glossary
Glossary-5
