Random Access Memory

Often referred to by the acronym RAM, this is the portion of a computer's circuitry where frequently accessed data is stored. A copy of Windows, and copies of running programs are stored here (they are copied from the hard disk when the program starts), along with the intermediate results of the program's calculations, etc. 

The contents of RAM are erased when the computer is powered off. So any data that must be remembered after the computer is turned off must first be copied to a more permanent (though usually slower) storage location, such as a hard disk.