Random Access Memory is a temporary (or volatile) storage space in the computer. It has very fast read write speeds which makes it ideal for storing programs when they are running. Typical capacities are between 2 and 8 GB although this is increasing all the time.
Read Only Memory is permanent (read only) storage space. It contains the BIOS which is required for the basic operation of the computer and tests the hardware to ensure the computer is ready to load. The bootstrap loader will then load the operating system into RAM.
ROM is located on the motherboard and is very small (eg 2Mb)
When RAM is full, the hard drive can be used as an extension to RAM for programs that are running. The hard drive has slower read write speeds which means that programs will run more slowly. For this reason, additional RAM can speed up the computer.
Q. Why is RAM or Internal Memory required in a computer system if data can be stored on the hard drive?
The hard drive has a slow read/write speed and so cannot keep up with how quickly data is required by the processor. RAM has a faster read/write speed and so programs and data can be stored here when in use to allow faster transfer of data.
In order to speed up the transfer of data even more, a tiny amount of volatile storage called internal memory or cache is used to store that that is just about to be used. Internal memory has super fast read/write speeds and so allows the processor to access data as fast as possible.
Data that is actually being processed is stored in registers on the CPU. When data is no longer required, it is passed back down the line to the internal memory, then RAM and finally to the hard drive.