Webopedia on Google+Webopedia on TwitterWebopedia on FacebookTech Bytes Blog
Main » TERM » C »

cache

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 computeravoids 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 CPUand 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.







TECH RESOURCES FROM OUR PARTNERS
DID YOU KNOW?
The Great Data Storage Debate: Is Tape Dead?

Tape clearly is on the decline. But remember, legacy systems can hang for a shockingly long time. Read More »

Apple Pay Promises to Strengthen Payment Security

Experts believe that Apple Pay and other competitive payment systems will be far more secure than cards, even cards equipped with EMV chips. Read More »

Internet of Things Shaping IT's Future

To make the IoT both work and pay off, IT is juggling upgrading and building app-centric networks, mapping out new data center architectures and... Read More »

QUICK REFERENCE
Webopedia Polls

The trend for the past two years has been for shoppers to spend more online during the holiday season. How do you typically shop for holiday... Read More »

How to Create a Desktop Shortcut to a Website

This Webopedia guide will show you how to create a desktop shortcut to a website using Firefox, Chrome or Internet Explorer (IE). Read More »

Flash Data Storage Vendor Trends

Although it is almost impossible to keep up with the pace of ongoing product releases, here are three recent highlights in the flash data storage... Read More »