In addition to the processor, a critical computer component is memory. As with humans, there is short-term memory and long-term memory. Long-term memory is represented by the hard-disk (to be covered in a future article. Computers keep short-term stuff in RAM (Random Access Memory).
RAM is not really accessed randomly – the term is more concerned with the fact that the computer can split all of this short-term storage into pigeon-holes and stick data temporarily where it likes. Being logical machines, the process is not random at all. In fact, short-term memory gets pre-allocated in large chunks to particular uses. For example, Microsoft Windows itself (the operating system) will reserver a wad of RAM for its core software, and another wad for recently-used data, and another wad kept spare for 'new' activities like starting another application.
Press Ctrl-Alt-Del (ie. the Ctrl, Alt and Del keys all at the same time) in Windows and you bring up the Task Manager window. Useful for seeing what applications are running (in the Applications tab), it has a number of vaguely interesting tabs. One of these is Performance, where you can see how busy your processor is (100% is flat out), and how much short-term memory is being used. You can see here the Kernel Memory reserved for the Windows operating system, and in the Physical Memory area you can see how much RAM the system thinks it has, of which some is available and some is for the System Cache.
All fascinating of course, but not something you can play with much. Fundamentally, computers like RAM – the more the better. A key concept is the 'paging file', used in many different operating system besides Windows. If the operating system needs more RAM than is available, there are two choices – stop doing stuff, or make-believe there is more RAM by temporarily storing some of the less-used RAM data onto the hard-disk. A big file (several hundred megabytes) is created on the disk within which RAM data can be stored if need be. However, the hard disk is much much slower than RAM, so having to use this paging file is terrible for performance. And if the computer has to use the paging file a lot, it can end up 'thrashing', where it is so busy putting stuff into and taking stuff out of the paging file that it gets nothing done at all.
The upshot is that you do not want your computer to need or use the paging file. Accordingly, the bigger the RAM available, the less chance of needing the paging file. At what point this occurs is very much dependent on the operating system (even which version of Windows) and what you do on it (eg. Microsoft Word soaks up well over 20 megabytes itself). For current Windows XP systems, you should have 512 megabytes and can expect slow performance with 256 megabytes. The new Windows Vista will likely double these requirements.
What actually gets stored in RAM other than core operating system programs and data? Well, anything you are looking at on your screen. Create a new document, it is only in RAM until you click the “Save” button (which naturally you do every couple of minutes to avoid disaster). Open a web-page, it is in RAM while you look at it. All the programs you have opened (and the files you may open within them) are put into RAM so you can switch from one to another quickly. All the stuff, in other words, that would not reappear if you suddenly unplugged the computer and then powered up again (or Unelco did it for you). RAM is good – but don't depend on it.
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