Random-access memory

Random-access memory (or simply RAM) is the memory in a computer that is used for running programs and storing data for the running programs. Data (information) in the RAM can be read and written quickly in any order. Normally, the random-access memory is in the form of computer chips. Usually, the contents of RAM are accessible faster than other types of information storage. However, RAM is volatile, which means that every time the computer is turned off, all the data in the RAM is lost. The alternative to this, Non-volatile random-access memory (NVRAM), which keeps its data without using power, is more expensive and works slower, so it is used in smaller amounts.

A stick of DDR3 RAM that is for laptops

Since the late 20th century, RAM uses transistors, usually MOSFETs, to store data. Before that, magnetic memory was the usual kind.

Different types of RAM

Dynamic random access memory (DRAM) is the majority in computers. Modern computers use several types of DRAM. Before 2002, most computers used single data rate (SDR) RAM. Most computers made since that time use either double data rate (DDR), DDR2, DDR3, DDR4, or DDR5 RAM. As the technology has progressed, it has allowed stored data to be moved and used more quickly, so that the computer's processor can keep working quickly without having to wait for data as long or as often.

Different generations of RAM will not work together in the same computer. Different generations of RAM have differently shaped connectors. This limits which RAM sticks a particular motherboard can use.

Static RAM (SRAM) needs power to keep its data, but does not need the computer to be active. Some SRAM chips are battery-backed. This type has a built-in battery to make sure no data is lost if the computer is turned off. Some computers have a little SRAM and mostly DRAM.

Other uses for RAM

RAM is usually used to store information of running programs inside computers. RAM may also be used for different things.

Virtual Memory

Using virtual memory, a computer can combine permanent storage with RAM to create a bigger pool of storage. This is useful when the RAM does not have enough space to store any more information. The extra data is then placed in the permanent storage instead of the RAM. The method has a limitation, which is that permanent storage is often slower than RAM, which can slow down a computer.

RAM disk

A computer can use a part of the RAM to store permanent files. This is called a RAM disk. When the computer is turned on, files are copied to the RAM disk. This allows the files to open faster because RAM is faster than permanent storage. When the computer is turned off, the information on the RAM disk is lost, which is why the files need to exist on permanent storage as well.

Other kinds of memory

Information that the computer always needs, that cannot be changed or deleted (unless it is EEPROM), is normally kept in read-only memory (ROM), which does not lose its contents when the computer is turned off. Such items include the BIOS (Basic Input/Output System), which stores the most basic commands for the computer, telling it how it should start up. The BIOS also tells the computer how to input and output information. The BIOS can be compared to the part of your brain that tells your heart how to beat. This is an important part.

Common Confusion

Random-access-memory (RAM) is not to be confused with Ram, as in the male sheep.