What is a computer? The most basic description is that it is a collection of hardware (and applicable software) comprising these three main components:

• A Central Processing Unit The main "brain" of the computer. With exceptions, controls and coordinates the entire functioning of the system. Here are some examples:
  • 8080/Z80/8088
  • 80286
  • 80386/80486
  • Pentiums, K6, etc.
• Memory/Storage There are many types-the main difference is access speed and whether it is volatile or not. Here are some examples:
  • Permanent/Non-volatile-does not disappear when you turn off computer.
    • Harddrives
    • Jazz /Zip drives
    • Tape and floppy drives
    • Solid State ROM memory
  • Volatile-goes away when you turn the computer off.
    • Solid State memory: RAM, DRAM, SRAM, etc.
• Input/Output
  • Keyboard
  • Mouse
  • Video displays
  • Printers
  • Modems
  • Scanners

How does it work?

• First, the computer must already have stored on it, the software that allows it to start (System software or the "operating system") and the software ("application software") that allows users to do useful work.
• The computer starts ("boots") up to some point that allows the user to perform useful work. In the case of DOS that's usually the C> prompt while in Windows it's getting to the desktop.
• When a user then runs a program from this point, the following events occur:
  • The operating system software fetches a copy of the program from where it is permanently stored on the hard drive and loads it starting at a specific address in RAM. All computers run their software from RAM because it has the fastest access time of any of the above listed types of memory.
  • The CPU then jumps to that address in RAM and begins executing ("running") the program.
  • The program, via the CPU, talks as needed to the I/O devices (The keyboard, mouse, video display, printer, etc.) and it may create and write data files back to the hard drive.
  • Upon program completion, the user is returned to the startup point-the C> prompt etc. where the computer waits for further input.

But what if I'm running Windows? Then you can have multiple programs ("processes") running at the same time...and it all gets a lot more complex!

Summary That, in a nutshell, is how your computer works at the most basic level. Once we get into the specific technologies of how each main component listed above is actually implemented (and how it all works together or not) on your system is when the fun really starts!

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