Features

Even seasoned computer users are sometimes unclear about the exact roles of memory (RAM) and the hard disk in the operation of a PC.That's partly because the distinction between their functions has become blurred.

In principle, the hard disk is where programs and data are stored - much like a human being's memory, rather confusingly! - while RAM is where your PC does its thinking. RAM stands for 'random access memory'; the 'random' part simply means the system's main processor (also known as a CPU, for 'central processing unit') can immediately read or write data to any part of memory. 'Loading' or 'launching' a program means copying it from the hard disk into RAM, where the processor can run it - that is, execute the instructions it contains. Because programs exist to manipulate data, in one way or another, those instructions mainly involve reading and writing data in RAM. When the power is turned off, everything in memory disappears, ready to start afresh next time. That's why you need to 'save' your work to the hard disk for storage.

Virtual memory

All quite straightforward. But ever since PCs gained the ability to run several programs at once, the amount of RAM available has often been insufficient to hold them all. So Windows constantly checks to see which bits of which programs, and the data they're working on, aren't being used right now, and swaps them out to an area of the hard disk. This 'virtual memory' provides more room than RAM, but works a lot slower. The more your hard disk has to contribute, the slower things get. And if the disk itself isn't running at its best, your PC can pretty much grind to a halt.

The size of your virtual memory swapfile is normally adjusted automatically by Windows - you'll sometimes see a message letting you know this is happening - but is generally between one and two times the size of the RAM installed. That means you'll need a few gigabytes of disk space free, and in fact around 10GB is a sensible minimum.

Making room

If you're running out of space, use the Programs and Features Control Panel (or Add/Remove Programs in Windows XP) to uninstall any programs you no longer use, including trial versions that have expired. Then delete any work files you don't need. To find files that are hogging space, try doing a search for files over a certain size - say, 10MB - to check for any big ones you can lose, and search for files with the extension '.zip', which are often downloaded installers that are no longer required. Remember to empty the Recycle Bin to reclaim the space taken up by deleted files. If you have folders full of data that you need to keep but won't use regularly, such as old work projects, compress them using software such as WinZip (www.winzip.com) or copy them onto recordable CDs or DVDs before deleting the originals.

If you can't make enough room, buy an external USB 2.0 hard disk. They're great value per megabyte, and require no installation except plugging in. Move as much as possible of your work onto this, leaving programs and speed-critical data, such as databases or video footage you plan to edit, on the internal drive.

Just make sure you don't move or delete a file unless you know what it is. Windows and other software use thousands of extra files that need to stay where they are to keep things working.

	1 Having programs installed that you don't use can be a big waste of space. Use the Programs and Features Control Panel to remove them, using the option to 'Turn Windows features on or off' to remove unnecessary Windows components.

	2 Launch Disk Cleanup by clicking Start > All Programs > Accessories > System Tools > Disk Cleanup. Choose between cleaning up your own files or those of every user (if you have more than one user account on your PC). After a quick system scan, Windows will list any files that can be safely removed.