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cache
Last modified: Thursday, September 16, 2004 

cache
Pronounced cash, a special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching.

A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.

Some memory caches are built into the architecture of microprocessors. The Intel 80486 microprocessor, for example, contains an 8K memory cache, and the Pentium has a 16K cache. Such internal caches are often called Level 1 (L1) caches. Most modern PCs also come with external cache memory, called Level 2 (L2) caches. These caches sit between the CPU and the DRAM. Like L1 caches, L2 caches are composed of SRAM but they are much larger.

Disk caching works under the same principle as memory caching, but instead of using high-speed SRAM, a disk cache uses conventional main memory. The most recently accessed data from the disk (as well as adjacent sectors) is stored in a memory buffer. When a program needs to access data from the disk, it first checks the disk cache to see if the data is there. Disk caching can dramatically improve the performance of applications, because accessing a byte of data in RAM can be thousands of times faster than accessing a byte on a hard disk.

When data is found in the cache, it is called a cache hit, and the effectiveness of a cache is judged by its hit rate. Many cache systems use a technique known as smart caching, in which the system can recognize certain types of frequently used data. The strategies for determining which information should be kept in the cache constitute some of the more interesting problems in computer science.

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For internet.com pages about cache . Also check out the following links!

Related Links

BIOS Settings - Advanced Chipset Features 
Extensive information on the settings associated with fine-tuning control over the system cache, memory, and I/O buses, to optimize performance. This page is from "The PC Guide".

Caching Tutorial for Web Authors and Webmasters 
A must read for anyone interested in Web caches.

PC secondary cache reference guide 
Looks at the secondary cache on the PC motherboard. Describes how the cache works in detail. Discusses cache characteristics, timing, technology types, packaging, and structures.

"Layers" of Cache
Description of Level 2 and 3 cache, as well as disk and peripheral cache. This page is from "The PC Guide".

Cache and the Web
Digital and the National Library for Applied Network Research (NLANR) are working together to create a national architecture for handling highly popular information (the internet). This page describes that effort, as well as provides numerous links to this work and research.

Cache Characteristics
Describes the different features of the level 2 cache. This page is from "The PC Guide".

Cache Structure and Packaging
Describes the different types of packaging that cache is normally found in. Includes information about integrated Level 2, daughterboard, and motherboard cache, as well as COASt (Cache On A Stick) modules. This page is from "The PC Guide".

Cache Transfer Technologies and Timing
Describes the factors that directly influence the performance of the level 2 cache, including cache bursting and pipeline burst cache. Also included is information on system timing and a comparison of transfer technology. This page is from "The PC Guide".

Function and Operation of the System Cache
Discusses the principles behind the design of cache memory, and explains how the secondary (level 2) cache works in detail. This page is from "The PC Guide".

Managing Netscape cache
Provides several tips for controlling the amount of disk space set aside for the Netscape browser's cache.

What is a cache?
Describes what level two cache is and how it works.

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related categories

Caches

Performance

related terms

buffer

buffer underrun

CDN

CELP

COAST

connection pool

disk cache

main memory

pipeline burst cache

proxy cache

RAM disk

snooping protocol

tag RAM

write-back cache


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