PCs / Microprocessors - Notes 2

Definition of "cache" from www.webster.com.

Main Entry: 1cache
Pronunciation: 'kash
Function: noun
Etymology: French, from cacher to press, hide, from (assumed) Vulgar Latin coacticare to press together, from Latin coactare to compel, frequentative of cogere to compel -- more at COGENT
Date: 1797
1 a : a hiding place especially for concealing and preserving provisions or implements b : a secure place of storage
2 : something hidden or stored in a cache
3 : a computer memory with very short access time used for storage of frequently used instructions or data -- called also cache memory
cache memory
Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.

Cache memory is sometimes described in levels of closeness and accessability to the microprocessor. An L1 cache is on the same chip as the microprocessor. (For example, the PowerPC 601 processor has a 32 kilobyte level-1 cache built into its chip.) L2 is usually a separate static RAM (SRAM) chip. The main RAM is usually a dynamic RAM (DRAM) chip.

In addition to cache memory, one can think of RAM itself as a cache of memory for hard disk storage since all of RAM's contents come from the hard disk initially when you turn your computer on and load the operating system (you are loading it into RAM) and later as you start new applications and access new data. RAM can also contain a special area called a disk cache that contains the data most recently read in from the hard disk.