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[ The PC Guide | Introduction to the PC | How the PC Works | How the Computer Computes ]

Human Instructions and Computer Instructions

An exercise: sort the following letters into alphabetical order: G B Y R V O. Most people can perform this task in 5 to 10 seconds. A modern PC can do it in less than 1/1000th of a second. Is the PC smarter? No, not even close. In fact, the PC doesn't know how to sort anything at all. A processor only understands a few limited instructions, which are usually quite primitive: for example, a processor can multiply two numbers, or make a decision based on the result of comparing a number against another one. All programs you use on your PC are built from these mathematical "building blocks", even though their complex appearance makes this difficult to believe.

To get the computer to be able to sort the letters, someone has to write a program that is constructed from the processor's simple building blocks and performs the task that is needed. Once this is done, the computer can do the work so quickly because it has such raw speed: processors can execute many millions of instructions a second. The computer is not something to be compared to a genius, but more to a hard worker that has to be shown specifically how to make something but then can make it incredibly rapidly.

Let's take our letters again: G B Y R V O. Now, instead of sorting them alphabetically, I will tell you that each is the first letter of a common color, and I'd like you to sort them in the order you'd find them in a rainbow. A human can adapt to this changed task and perform it in less than a minute; but for the computer, it's a totally different matter! The program written to sort the letters has no idea about colors, and has no way to start viewing the letters in that way. To accomplish this new task, a totally different program would have to be written, which would have to include information about colors and their names, what a rainbow looks like, etc. Now once written, the computer could sort these six letters from any random order you chose, a thousand times a second! But until it was written, the PC's response to being asked to perform this task would be the computer equivalent of "Huh?". As you can see, humans and computers excel at very different types of tasks, and the computer can only do what it is programmed to do.

One more thing: if I ask you to theorize as to the probable cause for the extinction of the dinosaurs, you can use your accumulated experience and knowledge, combine them with your personal beliefs, and give an answer. A computer not only couldn't give an answer, it wouldn't know where to start trying to figure it out, and there is no programmer on the planet that could make it perform this type of "computation" at all. There are some things that computers just cannot do at all--yet.

Next: Computer Languages

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