History of RAM

RAM is called random access because any storage location -- also known as a memory address - can be accessed directly. Originally, the term distinguished regular core memory from offline memory, usually on magnetic tape in which an item of data could only be accessed by starting from the beginning of the tape and finding an address sequentially. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations. Note that other forms of storage -- such as the hard disk and CD-ROM -  are also accessed directly or randomly, but the term random access is not applied to these forms of storage.

RAM started out as asynchronous, or having a different clock speed for the microchips in the RAM than the processor. This was a problem as processors became more powerful and RAM couldn't keep up with requests for data from the processor. In the early 1990s, clock speeds were synchronized with the introduction of synchronous dynamic random access memory. SDRAM reached its limit quickly, since it transferred data in a single data rate. Around the year 2000, double data rate random access memory (DDR RAM) was developed. This moved data twice in a single clock cycle -- at the start and end. The introduction of DDR RAM also seems to have changed the definition of SDRAM, as many sources now define it as single data rate RAM.

DDR RAM has evolved three times, through DDR2, DDR3 and DDR4. Each iteration improved data throughput speeds and reduced power use. However, each version is not compatible with the previous ones, as data is handled in larger batches in each innovation.