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Glossary–6
21264/EV68A Hardware Reference Manual
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
One status item for a cache block. The cache block is valid and has been written so that
it may differ from the copy in system main memory.
dirty victim
Used in reference to a cache block in the cache of a system bus node. The cache block
is valid but is about to be replaced due to a cache block resource conflict. The data must
therefore be written to memory.
DMA
See direct memory access.
DRAM
Dynamic random-access memory. Read/write memory that must be refreshed (read
from or written to) periodically to maintain the storage of information.
DTB
Data translation buffer. Also defined as Dstream translation buffer.
DTL
Diode-transistor logic.
dual issue
Two instructions are issued, in parallel, during the same microprocessor cycle. The
instructions use different resources and so do not conflict.
ECC
Error correction code. Code and algorithms used by logic to facilitate error detection
and correction. See also ECC error.
ECC error
An error detected by ECC logic, to indicate that data (or the protected “entity”) has
been corrupted. The error may be correctable (soft error) or uncorrectable (hard error).
ECL
Emitter-coupled logic.
EEPROM
Electrically erasable programmable read-only memory. A memory device that can be
byte-erased, written to, and read from. Contrast with FEPROM.