All computers contain a chip called a microprocessor, or CPU, which is responsible for controlling the computer's actions. Macintoshes have used Motorola's 68000, 68020, 68030, 68040, and PowerPC microprocessors. Many programs (for example, Dark Forces) were designed for at least the top-of-the-line chip in the 68000 family (the 68040) to take advantage of the powerful new features which it provides. Unfortunately, this prevents users of '020 and '030 Macs from using the software. Pseud040 is a shareware program for users of 68020 and 68030 Macs which installs a "virtual 68040" and allows them to run software which otherwise would require a 68040.