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Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk.

Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.

There are several different types of memory:

  • RAM (random-access memory): This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.
  • ROM (read-only memory): Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to.
  • PROM (programmable read-only memory): A PROM is a memory chip on which you can store a program. But once the PROM has been used, you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are non-volatile.
  • EPROM (erasable programmable read-only memory): An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.
  • EEPROM (electrically erasable programmable read-only memory): An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge.

  • More Information

    Outstanding Page Kingston Memory Guide
    Home page of a detailed site that described how memory works and discusses the differences between different types of memory. Includes descriptions of SIMMS, DIMMS, EDO DRAM, SDRAM, and more.

    Outstanding Page Memory Errors, Detection and Correction
    Describes the facilities available for doing error detection and correction and discusses what some of the important factors are. This page is from "The PC Guide."

    Outstanding Page PC Mechanic - online guide to computer hardware
    Contains overviews, purchasing and installation information for PC motherboards, memory, drives, expansion cards, and power supplies. Also contains links to companies and manufacturers and PC hardware related links. Updated on Aug 5, 1998

    Outstanding Page System Memory Overviews
    Describes memory technology types, memory speed, access and timing, DRAM technologies, memory size and packaging, errors, detection and correction, and logical memory layout. This page is from "The PC Guide".

      IBM memory products page
    Offers access to current information on IBM's memory product line, including datasheets and application notes. Updated on May 19, 1998

      Logical Memory Layout
    Describes how memory is allocated and how it is used within the PC. This page is from "The PC Guide".

      Memory Access and Layout
    This is Chapter 4 of Randall Hyde's book, "Art of Assembly Language." It describes how the 80x86 CPUs access data in memory. Updated on Aug 5, 1998

      Memory Packaging
    Describes the types of memory packaging available and the issues involved in selecting and using memory packages and DRAM chips in a PC. This page is from "The PC Guide."

      Memory Speed, Access and Timing
    Describes how the system memory works. Includes details on how memory is accessed and important issues related to system timing. This page is from "The PC Guide".

      Memory Technology Types
    Describes the main types of memory used in PCs (ROM, RAM, SRAM, and DRAM) and how they differ from each other. This page is from "The PC Guide".

      PC Guide's system memory reference
    Extensive reference covering the system memory. Covers technology types, memory speed and timing, packaging, error detection and correction, and the logical memory layout.

      System Organization
    This is Chapter 3 of Randall Hyde's book, "Art of Assembly Language." It describes the basic components that make up a computer system: the CPU, memory, I/O, and the bus that connects them. Updated on Aug 5, 1998

      Troubleshooting the System Memory
    Describes memory-related problems, referring specifically to the main system memory. This page is from "The PC Guide."

      Ultimate Memory Guide - Introduction
    Tutorial about what computer memory is, and how it differs from storage, and how much you need.

      Yahoo!'s memory page
    Yahoo!'s directory of memory. Updated on Aug 4, 1998

      Yahoo!'s memory retailers page
    Yahoo!'s directory of memory retailers. Updated on Aug 1, 1998


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