Computer memory and storage

Computer memory is where a system holds data and instructions, and it comes in several kinds suited to different roles. The most general distinction is between memory used for working storage while the computer runs and memory used to keep data permanently. RAM (random access memory) is fast, volatile working memory that loses its contents when power is removed, whereas ROM (read-only memory) retains its contents without power and holds fixed code such as start-up routines. Variants like EPROM can be erased and reprogrammed, blurring the line between fixed and changeable storage.

Storage capacity is measured in bits and bytes, with larger amounts expressed in kilobytes, megabytes, gigabytes, and terabytes, each roughly a thousand times the last. These units describe everything from the size of a memory chip to the capacity of a disk. A processor reaches memory and devices over a bus, and supporting chips such as the chipset coordinate the flow of data between the CPU, memory, and the rest of the system.

For permanent storage, computers use a range of devices. A hard disk records data magnetically on spinning platters, organised into tracks, cylinders, sectors, and clusters, and managed by a controller over interfaces such as IDE or SCSI. Optical media including the CD-ROM and DVD store data as patterns read by a laser, while solid-state and flash memory keep data in chips with no moving parts. The first sector of a bootable disk, the boot sector, holds the code that starts the loading of an operating system.

Frequently asked questions

What is the difference between RAM and ROM?

RAM is fast, volatile working memory that loses its contents when power is removed, while ROM keeps its contents without power and typically holds fixed code such as start-up routines.

How is storage capacity measured?

Capacity is counted in bits and bytes, with larger quantities expressed in kilobytes, megabytes, gigabytes, and terabytes, each roughly a thousand times larger than the previous unit.

How does a hard disk store data?

A hard disk records data magnetically on spinning platters divided into tracks and sectors, with a controller managing reading and writing over an interface such as IDE or SCSI.