(1) See memory card and flash memory.|
(2) The computer's workspace, which is physically a collection of dynamic RAM (DRAM) chips. A major resource in the computer, memory determines the size and number of programs that can be run at the same time, as well as the amount of data that can be processed instantly.
It All Takes Place in Memory
All program execution and data processing takes place in memory, often called "main memory" to differentiate it from the memory chips on other circuit boards in the machine. The program's instructions are copied into memory from disk, tape or the network and then extracted from memory into the control unit circuit for analysis and execution. The instructions direct the computer to input data into memory from a keyboard, disk, tape, modem or network.
Calculate, Compare and Copy
As data are entered into memory, the previous contents of that space are lost. Once the data are in memory, they can be processed (calculated, compared and copied). The results are sent to a screen, printer, disk, tape, modem or network.
Memory Is An Electronic Checkerboard
Think of memory as a checkerboard, each square holding one byte of data or instruction. Each square has a separate address like a post office box and can be manipulated independently. As a result, the computer can break apart programs into instructions for execution and data records into fields for processing. See early memories and RAM.
Each checkerboard square of memory holds one byte. The contents of any single byte or group of bytes can be calculated, compared and copied independently. That is how fields are put together to form records and broken apart when read back in. On a disk, data are stored in sectors, typically 512 bytes long, that are the smallest unit that can be read or written by the drive.
Memory Does Not Remember
Oddly enough, the computer's memory does not "remember" anything when the power is turned off. So why do they call it memory? Because the first memory did "remember," but today's RAM chips do not, which is why files have to be saved before the application is ended. Although there are memory chips that do hold their content permanently (ROMs, PROMs, EPROMs, flash, etc.), they are used for internal control purposes and data storage, not for processing. To make it even more confusing, it is likely that memory in the future will again "remember" (see future memory chips).
The main "remembering" memory in a computer system is its hard disks, and although they are sometimes called "memory devices," many prefer to call them "storage devices" (as we do) in order to differentiate them from internal RAM memory.
Memory Can Get Clobbered!
Memory is an important resource that cannot be wasted. It must be allocated by the operating system as well as by applications and then released when not needed. Errant programs can grab memory and not let go, which results in less and less memory available to other programs. Restarting the computer gives memory a clean slate, which is why rebooting the computer clears up so many problems with applications.
In addition, if the operating system has bugs, a malfunctioning application can write into the same memory used by another program, causing all kinds of unspecified behavior. You discover these bugs when the system freezes or something weird happens all of a sudden. If you were able to look into memory and watch how fast data and instructions are written into and out of it in the course of just a single second, you would realize that it is a miracle it works at all.
Other terms for the computer's main memory are RAM, primary storage and read/write memory. Earlier terms were core and core storage. See dynamic RAM, static RAM and memory module.