In a computer, the term random access memory (RAM), often called simply memory, refers to ICs that store working data. The amount, and speed, of memory are crucial factors in determining what a computer can and cannot do.

Data Flow

The flow of data between storage media and memory is controlled by the CPU
Above figure shows how data moves in a computer among an internal hard drive, an external hard drive, and a CD-RW storage medium. This process is controlled by the CPU. When you open a file on any medium, the data goes immediately into the memory. The CPU, under direction of the microprocessor, manipulates the data in the memory as you work on the file. Thus, the data in memory changes from moment to moment.
When you hit a key to add a character, or drag the mouse to draw a line that shows up on your display, that character or line goes into memory at the same time. If you hit the backspace key to delete a character, or drag the mouse to erase a line on the screen, it disappears from the memory.
During this time the original file on the storage medium stays as it was before you accessed it. No change is made to that data until you specifically instruct the computer to overwrite it. When you’re done working on a file, you tell the microprocessor to close it. Then the data leaves memory and goes back to the medium from which it came, or to some other place, as you direct. If you tell the computer to overwrite the file on the medium from which it came, many programs send the new data (containing the changes you have made) to unused space there; the old data (as it was before you opened the file) stays in its old location. This is a safeguard, in case you decide to undo the changes you made.
All the data passing between the storage media and memory, and between the memory and the CPU, is in machine language. This consists of binary digits (bits) 0 and 1. But the data passing between you and the CPU is in plain English (or whatever other language you prefer), or in some high level programming language, having been translated by the machine into a form you can understand.

Memory Capacity

The maximum number of megabytes or gigabytes of data that can be stored in a computer’s memory is known as the memory capacity. The main factor that determines memory capacity is the number of transistors that can be fabricated onto a single memory chip. Other factors, such as microprocessor speed, have a practical effect on the usable memory capacity.
A gigantic memory is of little practical value if the microprocessor is slow. Nor is a fast microprocessor worth much if the memory capacity is too small for the applications (programs) you want to run. Most software packages tell you how much memory you need to run the programs they contain. They’ll often quote two specifications: a minimum memory requirement and a figure for optimum performance (approximately twice the minimum requirement). If possible, you should equip your computer with enough memory for optimum performance.
When buying a new computer, keep in mind that this year’s high-end machine may become next year’s ordinary one when it comes to popular software, and in a few years it will no longer be adequate to run many of the programs that will be available. If your computer lacks the memory to run a given application, you can usually add more. But this can only be done up to a certain point. Eventually, your microprocessor will no longer be able to run contemporary software at reasonable speed, no matter how much memory you have.
How much memory do you think your machine will require to run two or three of your favorite applications at the same time? Double or triple it, and you will come close to the amount you are likely to need for the next two or three years, or until you are overcome by the urge to buy a new computer again.