Random Access Memory (RAM)

Random Access Memory (RAM) is a type of semiconductor memory that provides temporary data storage area permitting the access of stored data (reading) and altering this data (writing). The term random implies that any memory location can be accessed irrespective of the previously accessed location. The name has become synonymous with volatile memory because the removal of power results in loss of data.

Since 1970, there has been the evolution of two main types of volatile memory based on different design philosophies. Dynamic RAM (DRAM) cells consist of charge-storage capacitors and driver transistors. The presence of a charge in the capacitor represents a logical 1, whilst the absence represents a logical 0. Since capacitors naturally discharge, this type of memory requires periodic refreshing. This requirement results in the overhead of additional refresh circuitry. One major disadvantage of dynamic RAM is that reading and writing cannot occur during refresh cycles.

The second type of RAM commonly available is Static RAM (SRAM) where each cell employs a flip-flop circuit to store either a logic 1 or logic 0. This type of memory is faster as there is no refresh cycle; however, its complexity means that fewer can fit on a square millimetre of silicon. Consequently, any application where low memory space and high speeds are required employs this type of memory.