Rapid Access Memory (RAM)
Memory refers to the temporary internal storage areas within a computer. The term memory is usually used as 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 drive.
The main type of memory and the most familiar to users is random access memory (RAM). RAM is the same as main memory. A computer can both write data into RAM and read data from RAM.
Every time we turn on a computer, a set of operating instructions is copied from the hard disk into RAM. These instructions, which help control basic computer functions, remain in RAM until the computer is turned off. 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 disappears. The contents of RAM are necessary for the computer to process data. The results of the processing are kept temporarily in RAM until they are needed again or until they are saved onto the hard disk or other storage device.
Storage capacity of RAM is measured in megabytes (MB) and Giga Bytes (GBs). A 64 MB RAM means that it can hold 64 million bytes of data (a standard A4 page of text typically holds about 2,000 bytes or characters of text). Other types of memory include
- ROM (read only memory): unlike RAM, ROM is non-volatile and only permits the user to read data. Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer.
- PROM (programmable read-only memory): a PROM is a memory chip on which you can store a program. 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.