In a computer system the main memory is RAM, which is electronic memory made up of semiconductor chips, (random access memory), this enables the data stored in memory can be accessed equally quickly.
As a RAM has no moving parts, this enables it to be very fast, working at the speed of electricity. When a computer is running, it is used to hold programs and data, frequently when it is copying them from a hard disk. If the power goes the data inside the RAM is lost, as a result it needs to be stored on either a hard disk or other storage before switching off the computer.
In a RAM the main property is capacity, which is the amount of data that can be stored. This is measured in either megabytes (MB) or gigabytes (GB). When a computer system is switched on, this is the capacity of bytes that it can hold in memory.
Below is a picture of RAM, which is used inside the computer system to hold programs and data: