Random Access Memory (RAM), also known as main memory, is an area in the computer system unit that temporarily holds data and instructions for processing and execution by the processor unit.
RAM operates like a chalkboard that is constantly being written on, then erased, then written on again. Therefore, the more RAM you have the more powerful and faster your computer will operate.
There are two important facts to know about RAM:
Most RAM are volatile meaning that its content is lost once the computer is shut down. An expensive type of RAM called Flash Memory exist, however it is used only in digital cameras and high-end portable computers.
RAM speed ranges between 60 and 80 nanoseconds. A nanosecond is one billionth of a second.
Read Only Memory (ROM) contain programs that are permanently stored into these electronic chips by the computer manufacturer. These programs contain instructions that tell the computer how to start-up and diagnose itself.
Complementary Metal Oxide Semiconductor (CMOS) holds data about the configuration of your computer system. This include the amount of RAM installed, the type of mouse, monitor, keyboard, and hard disk installed. Since these information differ from computer to computer it cannot be stored in ROM.
CMOS are low-consumption electronic chips that use very little power allowing them to operate on batteries for many years. This make it possible to retain contents after the computer is shut down. Unlike ROM however, CMOS content can be easily changed to reflect changes in the configuration of a computer system.
Virtual memory allow you to run programs that are larger than the amount of available memory. For example, suppose that you have a computer that contain only 8 MB of RAM, and suppose that you want to use at the same time two programs - a word processor-processing program requiring 4 MB of RAM and a spreadsheet program requiring 8 MB of RAM. You might suspect that you will run out of RAM but this will not happen since the operating system will create a virtual memory on your hard disk to accommodate both programs. This is illustrated by the following diagram.
