You mean the CPU?
That exchange will heat my temper from nice and cool to near a full boil in under three seconds. "The CPU" is not, and never will be, the proper name of the box part of the computer, when the main parts of the computer are the monitor, the keyboard and mouse, and the boxy part that all of the above plugs into. CPU stands for "central processing unit", which is, on most household desktop or laptop computers, your Pentium chip, your Celeron, your Athlon -- not the whole honking box, but the smartest and hottest chip inside the box.
The standard household desktop computer has a fuckton of a lot more stuff inside the box than just the CPU. The CPU is usually in the middle of a contraption called the "motherboard", which has all sorts of slots and widgets to plug stuff into so that the computer's main brain can access all the niftiness. There are also hard drives, floppy drives, CD/DVD drives, sound cards, video cards, modems, ethernet cards, hard drives, power supplies, fans, and more than enough cable to satisfy a bored cat for at least a week.
Unfortunately, the Modern Inaccurate Use of Technical Terms Commission has seized onto the term "CPU" and has redefined it to (erroneously) refer to the whole goddamn box. End-users referring to the whole goddamn box as "the CPU" will either be laughed out of town when they call it this in front of someone who knows their computer's ports from a hole in the sand, or billed accordingly.
There is no one commonly accepted Geek Term to call the whole goddamn box. "Box" works. "Tower" works. "This piece what I'm kicking vigorously" will do in a pinch, provided you're kicking the right bit at the right time. There are probably a few more, but "box" and "tower" are the most common. "Case" will do, though that generally refers to the outside part and not the inside part. ("Computer" even works too, as many geeks view monitor, keyboard, and mouse as easily replaced peripherals not important to the proper functioning of the unit itself.) But if you call it "the CPU", or, just as bad, call the whole thing "the hard drive", prepare to be laughed out of town.