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Glossary–18
21264/EV68A Hardware Reference Manual
WAR
Write-after-read.
word
Two contiguous bytes (16 bits) starting on an arbitrary byte boundary. The bits are num-
bered from right to left, 0 through 15.
write-back
A cache management technique in which write operation data is written into cache but
is not written into main memory in the same operation. This may result in temporary
differences between cache data and main memory data. Some logic unit must maintain
coherency between cache and main memory.
write-back cache
Copies are kept of any data in the region; read and write operations may use the copies,
and write operations use additional state to determine whether there are other copies to
invalidate or update.
WRITE_BLOCK
A transaction where the 21264/EV68A requests that an external logic unit process write
data.
write data wrapping
System feature that reduces apparent memory latency by allowing write data cycles to
differ the usual low-to-high sequence. Requires cooperation between the 21264/EV68A
and external hardware.
write-through cache
A cache management technique in which a write operation to cache also causes the
same data to be written in main memory during the same operation. Copies are kept of
any data in a region; read operations may use the copies, but write operations update the
actual data location and either update or invalidate all copies.