The main memory is the systems component of the computer, which holds data and instructions required for ongoing process. It receives this information from an input device or a secondary storage unit. The more memory you have in your computer, the more operations you can perform, i.e. the faster it works.
There are two types of main memory: RAM and ROM.
Read-only memory (ROM) is built into the computer and cannot be changed. It contains information and software (such as the operating system) that controls the computer's actions from start up to shut down. ROM is called nonvolatile memory because the memory chips do not lose their information when power to the computer is turned off.
Random-access memory (RAM) is used to store the information and instructions temporarily while data is being processing. RAM is also known as volatile memory because the information within the computer chips is lost when power to the computer is turned off. This kind of internal memory is also called read/write memory. Today's memory chips can each store up to 512 MB of data; a set of 16 chips on a RAM module can store up to 1 GB of data.