This article appeared in the April 2002 WYSIWYG newsletter.
Computer Programs
by Jerry Carson
There haven't been many questions for the column lately. I hope this means that everyone's computers are working great! I thought I would try something new. Each month we don't have a question (and I have time), I'll try to give an overview on how some aspect of your computer system works. This month, I'll try programs. In the future, maybe device drivers or networking.
How do programs work?
Contrary to popular belief, computers are VERY stupid. But they are great at following directions. That's what a program is, a set of directions for the computer to follow. Most computers "know" how to perform about 200 instructions. Even these are usually variations of 8 basic steps. These are: ADD, SUBTRACT, MULTIPLY, DIVIDE, STORE, LOAD, JUMP, and COMPARE.
Some computers will know a few more steps, but these are the most common.
So a little program like:
PRINT "Hello World"
gets broken into a series of steps:
LOAD "H"
JUMP to output routine
LOAD "e"
JUMP to output routine
etc, etc
This is OK because the computer can perform nearly a billion of these simple steps every second. It's no wonder that in a large program like a word processor or an operating system, there are a few (ok, sometimes a lot) of places where the computer is performing the wrongs steps. Remember, EVERYTHING has to be broken into one of the 8 basic steps. Programmers use compilers to translate programming languages that are a little more like English into these basic steps called INSTRUCTIONS, or MACHINE LANGUAGE.
Also, each manufacturer, and sometimes the same manufacturer, has a different set of INSTRUCTIONS for there particular computer. Some are compatible, like Intel and AMD, but others are not, like Apple and Intel. So programs that are translated into the MACHINE LANGUAGE for an Intel computer will probably run on and AMD but won't run on an Apple.
Next time I want to talk a little about a special program called the BASIC INPUT/OUTPUT SYSTEM or the BIOS. Every computer has one, isn't it time we find out what it does?
'Til next time,
The Expert
End of Article