RAM, that refers to Random Access Memory, is a computer storage media which may be accessed considerably quicker than a hard drive, because the data can be read randomly, skipping the bytes before the needed info is reached. On a web server, the RAM is employed to load scripts and web programs when they are executed, so the more RAM you can use, the more programs you shall be able to run simultaneously and the more people will be able to surf your sites without effect on the site’s/server’s performance. Different from a disk drive, however, the RAM is used for short-term storage purposes, since the information is lost as soon as the power is shut off. If you use a shared web hosting account, the physical memory which your scripts could use may be limited and can change according to what the other customers on the same machine use. Using a virtual or a dedicated server, on the other hand, you shall have a guaranteed amount of RAM which will not be used by anybody else even when you don't use it at a given time.