The key benefit of RAM

The key benefit of RAM over types of storage which need physical movement is that retrieval times are short and consistent. Short because no physical movement is required, and consistent because the time taken to retrieve a piece of data does not depend on its current distance from a physical head; it requires practically the equal amount of time to access any piece of data stored in a RAM chip.

Because of this speed and consistency, RAM is used as 'main memory' or primary storage: the working area used for loading, displaying and manipulate applications and data. In most personal computers, the RAM is not an essential part of the motherboard or CPU—it comes in the easily upgraded form of modules called memory sticks or RAM sticks about the size of a few sticks of chewing gum, which can be quickly detached and replaced when they become damaged or too small for current purposes. A smaller amount of random-access memory is also integrated with the CPU, but this is usually referred to as "cache" memory, rather than RAM.

The disadvantage of RAM over physically moving media is cost and the loss of data when power is turned off. For these reasons, almost all PCs have disc storage as "secondary storage". Small PDAs and music players (up to 8 GiB in Jan 2007) may allot with disks, but rely on flash memory, to retain data between sessions of use.