Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type of non-volatile computer memory. PRAM uses the unique behavior of chalcogenide glass, which can be "switched" between two states, crystalline and amorphous, with the application of heat. Recent versions can achieve two additional distinct states, effectively doubling its storage capacity. PRAM is one of a number of new memory technologies that are attempting to compete in the non-volatile role with the almost universal Flash memory, which has a number of practical problems these replacements hope to address.