RAM in the computer industry has 2 meanings, both relating to memory but each in a different context:
- The first explanation for RAM is Random Access Memory, this is the name that was given to the very first FET-based silicon memory. That technology and name are still used today. Random access refers to the memory's ability to access any memory cell directly, as opposed to sequential data storage systems such as a tape drive, where one must process data sequentially in order to reach a certain point.
Per definition, many of today's storage systems can be categorized as random access memory. A compact disk, a ROM chip and a hard drive are all random access storage systems.
- The second explanation for the term is Read And Modify. This definition is used to display the difference between RAM and ROM: Where the ROM memory can only be written to once, the contents of RAM memory can be (re)written many times.
Random Access Memory can be divided in 2 groups, based on how information is retained, namely DRAM and SRAM:
- DRAM or Dynamic RAM can store data as long as it's powered, but requires refreshing to retain data. It is a small, relatively simple circuit and is generally the slower form of the two. This type of RAM is mainly used as working memory.
- SRAM or Static RAM stores data as long as it is powered, does not need refreshing and is the faster form of the two. It is also the more expensive one, and is used mainly in CPU caches.
Today, the term Random Access Memory is mainly used to refer to a computer's main/working memory. It is the third fastest memory subsystem in your computer, after the CPU's L1/L2 caches. When you power up your computer, it will load the operating system into RAM and boot. When you run a program, the program code and data that it requires, will be loaded into RAM. Any task that has to be executed, must to be loaded into RAM before it can be processed by the CPU.
RAM is a volatile memory, which implies that all data in RAM is lost when you turn off your computer. That's why computers have a hard drive to permanently store data, and it is also the reason you shouldn't just turn off a computer by pulling the plug.