Volatile memory

Volatile memory, in contrast to non-volatile memory, is computer memory that requires power to maintain the stored information; it retains its contents while powered on but when the power is interrupted, the stored data is quickly lost - usually in less than a second.

Volatile memory has several uses, including as primary storage such as RAM (Random Access Memory) on a computer. In addition to usually being much faster than forms of mass storage such as a hard disk drive (typically in the order of 500 to 2000 times faster for sequential access), volatility can protect sensitive information to some degree, as it becomes unavailable on power-down. Most of the general-purpose random-access memory (RAM) on computers, smartphones, tablets, and other types of digitally controlled devices is volatile.

Types

There are two kinds of volatile RAM: dynamic and static. Even though both types need continuous electrical current to retain data, there are some important differences between them.

Dynamic RAM (DRAM) is very popular as primary storage, due to its cost effectiveness. DRAM stores each bit of information in a different capacitor within the integrated circuit, with a single transistor keeping the capacitor charged or discharged. DRAM chips need just one single capacitor and one transistor to store each bit of information. This makes it space efficient and relatively inexpensive.

The main advantage of static RAM (SRAM) is that it is much faster than dynamic RAM - typically 20 to 50 times faster, when factors such as the motherboard's bus overhead are considered. Its disadvantage is its high manufacturing price. SRAM does not need continuous periodic electrical refreshes, but it still requires constant current to sustain the difference in voltage between transistor pins. Every single bit in a static RAM chip needs a cell of six transistors, whereas dynamic RAM requires only one capacitor and one transistor. As a result, SRAM is unable to accomplish the vast storage capabilities of DRAM without becoming much more expensive. SRAM is most commonly used as the internal cache and internal registers of CPUs.