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Memory is a computerís way of storing data. Some data is needed at all times. Other data is only used while the computer is on, and erased after it is turned off. There are three main types of memory: RAM (random access memory), ROM (read-only memory), and disk memory (stored on a hard drive of floppy).

RAM is a fast semiconductor memory. One part of it can be accessed just as fast as another. It has many "mailboxes" of space where data can be written/read from. Each "mailbox" has a number, or address. The computer uses the dataís address to refer to it and access its information quickly. The computer can read, or fetch data from an address. Also it can write, or store to an address, replacing the previous contents with new data. RAM is fast enough to keep up with the microprocessor, therefore usually a program being executed is loaded into the RAM and run from there. There are two types of RAM- Static RAM (SRAM) and Dynamic RAM (DRAM). Static RAM stores data and keeps it there until its current is altered. Dynamic RAM must be refreshed frequently so it doesnít fade away.

Read-only memory can be read only (hence the name J ). ROM can usually not be written to or changed, although there are some exceptions. Some types of ROM can be erased and then rewritten. PROM (programmable read-only memory) is welded into special chips by manufacturers. PROM is used by the system during boot-up. ROM is never lost when the computer shuts off. ROM is used to store lookup tables, for firmware (software embedded into the hardware), character specs, and converters that change one form of data to another (for example, a letter to its ASCII value).

Disk memory is commonly stored on hard disks or floppy disks. Hard disks are fixed disks, they reside in the computer and are rarely removed. They can hold much more data and are faster than floppies. Floppy disks are removable media and can easily be written to and removed, allowing a fresh one to be put in. This allows you to easily transfer data between different computers, without having to move the hard drive or link the computers. Hard disks and floppy disks work similarly. They both have disk-shaped platters that hold data. This data can be accessed at any time, unlike tapes, which are sequential storage devices. A hard disk has many rigid platters stacked on top of each other (not touching), but a floppy disk has one flimsy disk.


Upgrading and Repairing PCs Scott Mueller

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