Computer memory includes RAM, virtual memory, cache, registers, and flash. RAM is fast but volatile, while virtual memory is a cheaper alternative. Cache speeds up data transfer to the CPU, registers hold data for the ALU, and flash is non-volatile and used in digital cameras and mobile phones.
Computer memory can refer to many types of memory within a computer but, typically, refers to random access memory (RAM). It is physically found on computer chips that are inserted into the computer’s motherboard. RAM is electronic, rather than mechanical; that is, it has no moving parts and therefore data access is very fast. Modern computers often have 256MB (megabytes) to 2GB (gigabytes) of RAM, although there are, of course, computers with more or less RAM. RAM is also volatile, meaning it is lost when the computer is turned off.
The expensive nature of RAM has spurred the creation of another type of computer memory called virtual memory. With virtual memory, slow performance is only observed when trying to use a program whose files are located in virtual memory. Basically, this slowdown is observed only when switching between programs. In this way, virtual memory often provides a cheaper alternative to RAM.
A third type of computer memory is cache. There are two types of caches. The primary cache, or level 1 cache, is built directly into the central processing unit (CPU) and ensures instantaneous availability of data that the CPU often needs. The secondary cache, or level 2 cache, is usually built on a memory chip, sits very close to the CPU, and has a direct connection to the CPU via a dedicated circuit. The secondary cache has a larger capacity than the primary cache. Cache basically speeds up the rate at which data moves from main memory to the CPU.
Registers are a fourth type of computer memory. These are units within the CPU that contain specific types of data, especially for the arithmetic and logic unit (ALU). A final group of computer memory is called flash. This is a type of solid-state rewritable memory. Examples of flash memory include BIOS and memory cards. Just like RAM, they are electronic and not mechanical. They are also non-volatile and are therefore suitable for digital cameras, mobile phones and other miniaturized computers.
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