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Cache and/or Cache Sockets
Virtually all newer 486 or Pentium class motherboards come with either integrated secondary cache or sockets for secondary cache to be inserted. Also called "Level 2" or "L2" cache, secondary cache is high-speed memory that is used to buffer processor requests to the regular system memory; it is discussed in some detail here. Either 256 KB or 512 KB of cache is most common, with larger sizes such as 1 MB and higher now coming onto the market. Motherboards for Pentium Pro and Pentium II PCs don't have level 2 cache on them; it is already integrated into the processor itself for the Pentium Pro, and into the processor package for the Pentium II.
Motherboards typically have either cache chips soldered directly into the board, sockets for cache chips, or a socket for COASt, or "cache on a stick". Yeah, it's really called that. :^) This socket is sometimes called a CELP ("card edge low profile"). It takes a module with cache chips on it, that looks something like a memory SIMM (except it is usually inserted differently into the motherboard). There are also motherboards that have both: they come with 256 KB of built-in cache and a COASt module for the addition of 256 KB more. These are now becoming less common with many companies deciding it is cheaper to just put 512 KB on the motherboard to begin with.
Having level 2 cache on the motherboard may eventually be a thing of the past. The trend is toward putting the L2 cache either on the chip itself (a la Pentium Pro) or on a daughterboard (Pentium II and future Intel processors).
Warning: Some motherboards,
in particular newer 486 PCI-VLB-ISA boards, have been showing up with false cache
on them. In some cases the BIOS is even doctored to "report" that it sees the
cache. See here for more details.
Next: I/O Bus Slots