FAST PAGE MODE DRAM

3/2/96

FAST PAGE MODE DRAM -- (Fast) Page Mode can speed up DRAM accessing somewhat when sequential memory accesses are made. It allows fast access to an open DRAM Page where Pages are typically 128 bytes or more (Roughly SQR(Size) /Width e.g. 1Megx8 = SQR(1024)/8=1024/8=128). The time specified for DRAM is the time required for an initial non-page mode access. A subsequent page mode access will require roughly 75% of the time needed for a non-page mode access. DRAM has a recovery time roughly the same as the DRAM non-page mode access. 60 nSec DRAM requires 60nSec (plus some non-RAM delays elsewhere in the circuitry) for an initial access; 60 nSec to recover; then 45 nSec for a subsequent Page Mode Access with 60 nSec recovery. Interleaving can often be used to "hide" recovery delays. Essentially all modern DRAMs support Fast Page Mode but 386 or older machines may not have Fast Page Mode DRAM, or may not support the mode by adjusting wait states on Page Mode DRAM Accesses. There is a penalty for changing pages. Page mode is primarily useful when it is known that subsequent memory references will be within the same page -- as when burst reading 4 word "lines" into caches.

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