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Repairing and Upgrading Your PC by Barbara Fritchman Thompson, Robert Bruce Thompson

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Chapter 6. Memory

Computers use memory, also called main memory or RAM (Random Access Memory), to store active programs—including antivirus scanners and other background services—and the data the system is using at the moment. Data can be written to and read from RAM extremely quickly—roughly a million times faster than a hard drive—but data in RAM is retained only while the system is running. RAM costs hundreds of times more than hard disk storage, byte for byte, so RAM is not an economically practical substitute for hard disk storage.

The characteristics of RAM and hard disk storage are complementary. The hard drive stores programs and data that are not currently being used, for which large capacity and permanence are important but speed is not. RAM stores active programs and data, for which access speed is important but smaller capacity and transience are not.

That's not to say that the amount of RAM you have installed in your computer is unimportant. Far from it. If your computer has insufficient RAM to hold all of your active programs and data, it slows down—sometimes dramatically. This problem occurs when the operating system must swap out active programs and data from memory to the hard drive to make room for other programs and data. In extreme cases, such as running Windows XP with several active programs in a ...

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