Types of Computer Memory

Memory is the computer hardware integrated circuits that store information for immediate use in a computer. Memory is distinct from the hard drive because it allows the CPU to immediately access the data it needs. Most forms of memory are temporary, they do not save data permanently.

Memory can be divided into two basic categories, volatile and non-volatile. Volatile memory’s distinguishing trait is it does not save data permanently; if power is interrupted, the data is soon lost. Volatile memory is used as primary storage, where data is stored temporarily rather than saved permanently to secondary storage. The greatest advantage of volatile memory is that it is faster than mass storage like a hard disk drive.

The most common type of volatile memory is RAM, or random-access memory. First used in the 1970s, RAM stores data and machine code being used and allows it to be read or written at the same time regardless of the physical location of data inside the memory. RAM does not suffer from mechanical limitations like media rotation speeds the way hard disks or CDs do.

RAM is further divided into two types, dynamic random-access memory and static random-access memory. DRAM is commonly used in PCs, workstations, and servers. DRAM stores each bit of data in a storage cell consisting of a capacitor and a transistor and requires a new electronic charge every few milliseconds to compensate for leaking charge from the capacitor. The benefits of DRAM are that it is simple to design, fast, and cheaper compared to other types of memory. However, it is volatile and consumes a lot of power. Static random-access memory uses a cell of six transistors in cross-coupled flip-flop configuration. Unlike DRAM, SRAM does not require a periodic refreshment. SRAM is faster but more expensive than DRAM, and often used for cache memory.

Another type of memory is non-volatile memory. Non-volatile memory can retrieve stored information even after power has cycled. Non-volatile memory typically takes the form of read-only memory, or ROM. ROM is used in computers and electronics, and is distinguished from RAM in that it cannot be electronically modified after manufacture, only read. ROM is typically used to store software that rarely changes over a system’s life, known as firmware. Firmware is usually low-level control of a device’s hardware, like a TV remote’s controls. ROM has further variations, such as programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), and electrically erasable programmable read-only memory (EEPROM).