If you upgraded from XP's forebear, Windows 2000, you know that its designers sacrificed some compatibility for stability; many Windows 9
x programs (games in particular) won't run on 2000. With XP, Microsoft made a largely successful effort to run older programs written for Windows 9
x and even Windows 3.1/DOS. But if XP has trouble running a program that ran fine in Windows 9
x, NT, or 2000, you can try tricking the program into thinking that it's running on the older OS.
To run a troublesome older program:
1. Right-click a program's executable (.exe) file or shortcut icon; then choose Properties > Compatibility tab (Figure 6.11 ).
2. Change the compatibility settings for the program; then click OK.
The next time that you open the program, XP tries to fool it into running.
Windows 3.1 and DOS programs are called
16-bit programs. Programs written for Windows 95, NT, and later are called
32-bit programs. The 16-bit programs run slowly because XP runs them in a leakproof, emulated space called a
virtual machine that draws on a common memory pool. If one 16-bit program crashes, they all crash. To run DOS programs, choose Start > All Programs > Accessories > Command Prompt. See also "Killing Unresponsive Programs" and "Using the Free Utility Programs" later in this chapter.
If XP displays an incompatibility message when you try to install or run a 16-bit program, don't ignore it. Either find a patch (update) or scrap the program.