DEC 4000 AXP Service Manual page 218

DEC VET
Digital's DEC Verifier and Exerciser Tool. DEC VET is a multipurpose system
maintenance tool that performs exerciser-oriented maintenance testing.
direct-mapping cache
A cache organization in which only one address comparison is needed to locate
any data in the cache, because any block of main memory data can be placed in
only one possible position in the cache.
direct memory access (DMA)
Access to memory by an I/O device that does not require processor intervention.
dirty
Used in reference to a cache block in the cache of a system bus node. The cache
block is valid and has been written so that it differs from the copy in system
memory.
disk fragmentation
The writing of files in noncontiguous areas on a disk. Fragmentation can cause
slower system performance because of repeated read or write operations on
fragmented data.
disk mirroring
See volume shadowing.
distributed processing
A processing configuration in which each processor has its own autonomous
operating environment. The processors are not tightly coupled and globally
controlled as they are with multiprocessing. A distributed processing
environment can include multiprocessor systems, uniprocessor systems, and
cluster systems. It entails the distribution of an application over more than one
system. The application must have the ability to coordinate its activity over a
dispersed operating environment. Contrast with symmetric multiprocessing.
DRAM
Dynamic random-access memory. Read/write memory that must be refreshed
(read from or written to) periodically to maintain the storage of information.
DSSI
Digital's proprietary data bus that uses the System Communication Architecture
(SCA) protocols for direct host-to-storage communications.
Glossary–8