Should you live with a minimum amount of RAM and save a few dollars, or should you spend some extra cash and load up the system? Just how much memory is enough? The answer really depends on what you're doing with the PC; RAM requirements can vary from system to system. Let's do the math.
Windows XP is rated to run with a minimum of 128MB, but it gets a real speed boost from 256MB. Windows 2000 puts its baseline at 64MB but will benefit from 128MB or more and as a server will see optimal performance with 512MB or more. Windows 98 and Me will run with 32MB, but you'll need at least 64MB for decent performance and 128MB or more to shine. Linux users will need at least 48MB to 64MB (depending on the version) but will certainly benefit from 128MB. For a Linux server, you could easily use 512MB or more.
Of course, the OS is useless without applications, so you'll also need enough memory to load all the programs you want to run at any one time. Applications like Microsoft Word or Excel generally use about 32MB each, but you can check the system requirements listed on each application's box to determine the recommended RAM. If you want to run three applications simultaneously (say, Word, Internet Explorer, and Media Player), you'll need to add the RAM requirements for all three to your total. Finally, you'll need RAM for data files—the open Word documents, Excel spreadsheets, MPEGs , and so on. More complex work demands more RAM. For example, a simple document may require less than 1MB, but a database file may fill several megabytes, and a high-resolution photo scan or graphic design may demand 50MB or more.
As a rule of thumb, if you base your overall memory requirements on the amount recommended for your operating system, you'll be in the ball park. As noted, you'll have to add more if you're processing large, complex files. Remember that Windows also uses virtual memory in the form of a swap file on your hard drive. If you don't want to buy the full amount of RAM that you expect to need, that's okay; your PC will make use of virtual memory to make up any difference. But be aware that this will result in a performance hit because of the hard drive access.