Cache on a stick

These modules were somewhat popular in the Apple and PC platforms during early to mid-1990s, but with newer computers cache is built into either the CPU or the motherboard.

COASt modules decoupled the motherboard from its cache, allowing varying configurations to be created.

COASt modules provided either 256K or 512K of direct-mapped cache, organized as 8192 or 16384 lines of 32 bytes.

The modules contained 256K or 512K of fast pipeline burst SRAM, plus 8 or 11 bits of even faster static RAM per line to store the cache tags.

A 512K module contains twice as many cache lines, and so requires one fewer tag bit to support the same cacheable memory size.

A COASt cache module and a quarter for size comparison. This module has room for a tag RAM on the left-hand side, but none is installed.
  1. CPU (Pentium 133)
  2. Tag RAM for L2 cache
  3. Socket for COAST Module