Phase-change memory (PCM) is a form of computer random-access memory (RAM) that stores data by altering the state of the matter from which the device is fabricated. According to its proponents, PCM technology has the potential to provide inexpensive, high-speed, high-density, high-volume nonvolatile storage on an unprecedented scale.
Because it is much closer in speed to dynamic RAM (DRAM), phase change memory technology is ideal for both non-volatile dual in-line memory modules (NVDIMMs) and non-volatile memory express (NVMe) solid state drives (SSDs). Apart from its speed advantage, phase change memory technology is also much more durable than flash, and any concern about the number of daily writes causing wear-out is not an issue. PCM is sometimes called "perfect RAM" (PRAM) because data can be overwritten without having to erase it first.
The structure of PCM material can change rapidly back and forth between amorphous and crystalline on a microscopic scale. In the amorphous or disordered phase, the material has high electrical resistance; in the crystalline or ordered phase, its resistance is reduced. This allows electrical currents to be switched on and off, representing digital high and low states. Because the physical structure is three-dimensional, the number of transistors that can exist in a chip of fixed size can be maximized, making it possible for PCM to function many times faster than conventional flash memory, while using less power.