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processor-memory gap

The huge difference between how fast a processor works and how slowly main memory answers: one trip to memory costs as long as hundreds of instructions.

The processor-memory gap is the ratio between processor cycle time and DRAM access latency; processor speed grew far faster than DRAM latency improved for decades, so a load that misses every cache now costs on the order of 100 ns, hundreds of cycles at multi-GHz clock rates.

See also

DRAM SRAM
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