PC Hardware A Beginner’s Guide

Adding cache memory to a system is like adding a refrigerator to your situation. If you

were able to purchase a six-pack or a case of your favorite drink, it would save you a lot of

sneaker wear and tear. Caching anticipates what the CPU may next ask for and copies the

equivalent of a case of data or instructions to cache memory. As long as the CPU requests

the data stored in cache memory, the whole system speeds up. Since, the caching system

guesses correctly about 90 to 95 percent of the time, caching saves a tremendous amount

of wait cycles for the CPU.

In order to increase the amount of level 1 (L1) cache on a PC, you have to replace the

CPU with a processor that is compatible with the motherboard and chipset that includes

additional internal L1 cache. On the other hand, level 2 (L2) cache can be upgraded. L2

cache modules are plugged into special cache module mounts or cache memory expansion

sockets located on the motherboard (more on this later).

Internal, External, and Levels of Cache

There are two types of cache memory:

 Internal cache Also calledprimary cache; placed inside the CPU chip

 External cache Also calledsecondary cache; located on the motherboard

As briefly touched upon already, cache is also designated by its level, which is an

indication of how close to the CPU it is. Cache is designated into two levels, with the

highestlevelofcachebeingtheclosesttotheCPU(itisusuallyapartoftheCPU,infact):

 Level 1 (L1) cache Level 1 cache is often referred to interchangeably with

internal cache, and rightly so. L1 cache is placed internally on the processor

chip and is, of course, the cache memory closest to the CPU.

 Level 2 (L2) cache Level 2 cache is normally placed on the motherboard very

near the CPU, but because it is further away than L1 cache, it is designated

as the second level of cache. Commonly, L2 cache is considered the same as

external cache, but L2 cache can also be included on the CPU chip. If there

is a level 3 to cache, it is RAM.

L1 and L2 cache, as well as internal and external cache, are not exactly levels in the

sensethatL1ishigherinrankingthanL2.Thedifferentlevelsofcacheworktogether,and

data is located in either level based on the rules and policies associated with the caching

system—more on these later.

In contrast to these definitions of cache memory’s placement and levels, older PCs,

notably those with 286 or 386 processors, do not include cache memory on the CPU. Any

cache memory on these PCs must be located on the motherboard and is designated

primary (L1) cache. Yes, this external cache is L1 cache. Not to worry; this is the exception

and it is dying as fast as these PCs.

(^160) PC Hardware: A Beginner’s Guide