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Random-access memory (RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). "Random" refers to the idea that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.
Random access memory is volatile memory, meaning it loses its contents once power is cut. This is different from non-volatile memory such as hard disks and flash memory, which do not require a power source to retain data. When a computer shuts down properly, all data located in random access memory is committed to permanent storage on the hard drive or flash drive. At the next boot-up, RAM begins to fill with programs automatically loaded at startup, and with files opened by the user. The word RAM is often associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. Many other types of memory are RAM, too, including most types of ROM and a type of flash memory called NOR-Flash. There are two different types of RAM:
DRAM (Dynamic
Random Access Memory) and SRAM (Static Random Access Memory). The two
types differ in the technology they use to
hold data, with DRAM being the more common type. In terms of speed, SRAM
is faster. DRAM needs to be refreshed thousands of times per second
while SRAM does not need to be refreshed, which is what makes it faster
than DRAM. DRAM supports access times of about 60 nanoseconds, SRAM can
give access times as low as 10 nanoseconds. Despite SRAM being faster,
it's not as commonly used as DRAM because it's so much more expensive.
Both types of RAM are volatile, meaning that they lose their
contents when the power is turned off.
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