Often confused with the hard drive, RAM stands for Random Access Memory and is the most common type of memory used in computers. A computer's RAM is the memory used to store data and programs on a temporary basis. The RAM is compared to short-term memory, as it stores applications and information that is actively used while the system is on. In comparison, the hard drive, the long-term memory, stores all programs and information permanently, whether the computer is on or not. The amount of RAM directly affects a computer’s performance. The more RAM a computer has, the more programs and documents it can have open without slowing the system down. Current PC computers have anywhere from 256 MB of RAM, or 256 million bytes of memory a program can use, to as much as 4 GB of RAM. Mac computers generally have between 128 and 512 MB of RAM.