CYBER NOTES September, 2004 by Dave Benore

Understanding The Boot-up Process

Last month was an overview of computer hardware. Let’s look a little closer at what happens inside of your computer when you turn it on.

When the electrical power is first turned on, the computer, in that instant, is totally dumb—without instructions of any kind. The act of power flowing into the computer causes it to “boot-up”. There is some physical wiring inside the computer that gives the computer its first instructions. Those instructions tell the computer where to look for more detailed instructions. Normally, the computer first looks at the floppy drive if it has one, then, if there is no floppy disk in the drive, it looks at the hard disk. (This sequence can be changed. The computer can also be directed to look at the CD drive.)

Where ever the computer first finds its boot-up instructions, it reads them and follows them. These instructions tell the computer how to test itself to see if everything is working properly. After testing, the boot-up instructions tell the computer where to find the configuration and operating system instructions. These tell the computer all about what is connected to it, how it should present information to the monitor, and how to “talk” with you, the operator. The configuration and operating system instructions are what are called “Windows” in PC land. (Mac computers use a different operating system but the principles are identical.)

At this point in the process the computer has been “trained” to communicate with the operator and the various devices connected to it. The computer, in the boot-up process, has gone from an “infant” to a “college graduate”! It now stands idle, waiting for the operator to tell it what to do next.

Each time the computer is turned on, this process repeats itself. Each time the computer is turned off; it “forgets” everything it learned before. But since the instructions are “written”, on the hard disk for example, the computer can reread them and come up to speed (boot-up) ready to serve.

This boot-up process normally uses three pieces of hardware discussed last month, the hard disk, RAM, and the CPU. (RAM means random access memory and CPU means central processing unit—not very glamorous terms.) Understanding these three pieces of hardware is critical to understanding how computes work.

The hard drive is many small spinning disks that have an extremely thin iron coating on them. This coating can be magnetized in separate very tiny spots. The pattern of how these tiny spots are magnetized create a “code”; one which the computer can understand. The instructions the computer gets from the hard disk are contained in this magnetic code. The code is “read” by very small sensors and turned into electrical impulses that are sent to the RAM.

The RAM stores the code for it is the active memory of the computer. It is very fast but is electrical in operation, not magnetic, so when the power goes off, RAM “forgets” everything it had stored in itself. Conversely, the hard disk does not forget anything when the power goes off.

The CPU, the “brain” of the computer, gets its instructions from RAM, processes them (does what it is told), and returns any responses (answers) to RAM—and repeats the cycle until all instructions have been completed. The responses show up on the computer’s monitor where the operator can see them.

An analogy of all this could go like this: The RAM and the CPU together are like the human brain. The human brain has memory (RAM) and can think (CPU). When the human brain needs more information it goes to a school or to a library (the hard disk is both). So computers are a little like people, except they go brain dead when the power goes off! Happy computing!