Optical,Magnetic,Solid state


optical memory was an early form of computer memory invented at the Mellon Institute in the 1950s. The device used a combination of photoemissive and phosphorescent materials to produce a "light loop" between two surfaces. The presence or lack of light, detected by a photocell, represented a one or zero. Although promising, the system was rendered obsolete with the introduction of core memory in the early 1950s. It appears that the system was never used in production, but it represents one of the typically odd earlier attempts to produce a useful high-speed memory system.


Magnetic-core memory was the predominant form of random-access computer memory for 20 years (circa 1955–75). It uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and read information. Each core represents one bit of information. The cores can be magnetized in two different ways (clockwise or counterclockwise) and the bit stored in a core is zero or one depending on that core's magnetization direction. The wires are arranged to allow an individual core to be set to either a "one" or a "zero", and for its magnetization to be changed, by sending appropriate electric current pulses through selected wires. The process of reading the core causes the core to be reset to a "zero", thus erasing it. This is called destructive readout.

Solid state

A solid-state drive (SSD) (also known as a solid-state disk or electronic disk, though it contains no actual "disk" of any kind, nor motors to "drive" the disks) is a data storage device using integrated circuit assemblies as memory to store data persistently. SSD technology uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives, thus permitting simple replacement in common applications. Also, new I/O interfaces like SATA Express are created to keep up with speed advancements in SSD technology


Optical: Disc drive

Magnetic: Credit card

Solid state: Memory stick