One observation that many computer owners make to me is that their PC seems to be running much more slowly than it did when they bought it. In some of these cases the reason is due to the machine being infected by spyware. But in many cases the machine is clean but is still running slower than it was originally. Usually it's easy to figure out why this is the case.
In order to cut costs, many PC manufacturers skimped on the amount of memory they fitted to PCs. This was particularly true 3-4 years ago, but still happens to some extent today, particularly with laptops. According to Microsoft, Windows XP will run on a machine with only 64MB of RAM and, to some extent, it will, but you will not have a PC that is usable. By and large, 128MB is the practical minimum that you need to run Windows XP. However, open more than two or three programs at the same time and again your machine will start to run extremely slowly. 256MB of ran is better but, to my mind, 512MB should now be considered the minimum amount of RAM to be fitted to a PC running Windows XP (note that Windows 98 and Me have a much more modest RAM requirement and can happily work with 64-128MB of RAM).
If a machine is running slower today than it was when purchased, it is probably down to the fact that there are more demands being made on the memory as a result of more programs loading into memory on startup. You can get an idea of how many programs are running by looking at your System Tray at the bottom right corner of your screen. The picture above shows the system tray of my laptop, which is pretty busy, indicating that I have quite a few programs running at the same time - many of these are running in the background and do not appear as active windows on the desktop. To check how much memory you have on your system and how much is being used at any point in time you want to open the Task Manager. You can do this by pressing Ctrl-Alt-Del which opens the Task Manager, which has a number of tabs. The tab you want to select is the Performance one, shown in the picture on the left. The section headed Physical Memory lists the amount of physical RAM on your machine under the Total heading - 523184 in my case, which corresponds to 512MB. The amount free at the time that I took the screenshot was ~73MB, which is just about 14%, not a lot. This is echoed by the fairly high PF (Page File) Usage figure of over 500MB. The Page File is an area on your hard disk that the system uses as virtual memory if the actual amount of physical RAM installed on the computer is becoming full. Because data is transferred much more slowly between the CPU and the hard drive than between the CPU and RAM, high PF Usage can lead to sluggish behaviour of the PC, and my laptop is not exactly flying at he moment. Time for either a clean out of un-needed programs or the addition of another 512MB of memory I think.
The bottom line is that upgrading your physical RAM to 512MB, or better still 1GB, is without doubt the most cost-effective way of improving the overall performance of your machine.