Specifications

Glossary GL–5
device See node and peripheral device.
differential I/O
module
A 16-bit I/O module with SCSI bus converter circuitry for extending a
differential SCSI bus.
See also I/O module.
differential SCSI
bus
A bus in which a signal’s level is determined by the potential difference
between two wires. A differential bus is more robust and less subject to
electrical noise than is a single-ended bus.
DILX Disk inline exerciser. The controller’s diagnostic software used to test the data
transfer capabilities of disk drives in a way that simulates a high level of user
activity.
DIMM Dual inline Memory Module.
dirty data The write-back cached data that has not been written to storage media, even
though the host operation processing the data has completed.
DMA Direct Memory Access.
DOC DWZZA-On-a-Chip. An NCR53C120 SCSI bus extender chip used to
connect a SCSI bus in an expansion cabinet to the corresponding SCSI bus in
another cabinet.
driver A hardware device or a program that controls or regulates another device. For
example, a device driver is a driver developed for a specific device that allows
a computer to operate with the device, such as a printer or a disk drive.
dual-redundant
configuration
A controller configuration consisting of two active controllers operating as a
single controller. If one controller fails, the other controller assumes control of
the failing controller’s devices.
dual-simplex A communications protocol that allows simultaneous transmission in both
directions in a link, usually with no flow control.
DUART Dual universal asynchronous receiver and transmitter. An integrated circuit
containing two serial, asynchronous transceiver circuits.
ECB External cache battery. The unit that supplies backup power to the cache
module in the event the primary power source fails or is interrupted.
ECC Error checking and correction.
EDC Error detection code.