A system unit is a computer housed inside your computer.
Following are just a few of the many functions that would typically be carried out by one or more system units within a desktop-type personal computer.
System processor—typically an Intel Pentium or AMD Athlon chip running at 3 to 6 gigahertz (/GHz) with two to four cores, managing all software processing.
MEMORY MECHANISM–providing random access memory so that programs can work on data temporarily before spilling them into larger storage files in, say, hard disk drives.
VIDEO CARD–producing images on the screen when there’s no external monitor plugged in; also holding special electronic circuitry (called “sprites”).