Boot - How does the initial self-test.

Boot - How does the initial self-test.

Turning on the computer, nothing important seems to happen for a few seconds. In fact, he is going through a
complex set of operations to verify that all components are functioning accordingly and warn you if something is not
is going well. This operation is the first step in a process somewhat complicated, called match (boot-up), or
simply boot. The term comes from the concept of you can stand on their own feet, or boots in case. On a PC,
This process is necessary because the machine must have a way to awaken all your components and thus load
the operating system without problems. Then the operating system takes care of tasks a little more complicated,
the boot code can not manage alone, including the equipment to interact with programs.

But even before the PC tries to load an operating system, it needs to make sure that all components
are running and the CPU and memory are working properly. This is the work of the initial self-test, or POST.
The self-test is the first thing that runs when the PC is turned on, and is the first to know when there are problems in any
components. When the self-test detects error on the monitor, the memory, the keyboard or a basic component, it
displays an error message on the screen and - if the monitor is one of the problems - shows where the error is, issuing a series
beep, or beeps. Normally, neither beeps nor screen message is sufficient to provide accurate information on the
what's wrong. Actually, what is meant by that is generically indicate which component is faulty.

A single beep combined with the appearance of the DOS message means that all components passed the self-test.
But any other combination of long and short beeps indicate a problem. Even the absence of beeps indicates that there is something wrong.

The following table shows how to interpret the beeps - the sign (.) Means short beep and (-) long beep - or lack of them.

Monitor beeps Area Problem None None None Only the cursor Energy Power No Message DOS Speaker
Message from DOS Normal Screen Disk BASIC Nothing Nothing Monitor Monitor error code number, in general, memory number
Error code 305 Keyboard Miscellaneous Anything Energy Bip continue Anything Anything Energy Board
System Monitor Anything Anything Monitor

If no error message or beep occurs, does not mean that all components are working fine. POST is capable of
check only the most common mistakes. He can tell you if a hard drive is not being supposedly installed
recognized, but can not detect if there is problem in formatting the disk. It was concluded that the POST is not so
useful. This is because the PCs work as safely rarely something triggers the alarm self-test. The
POST benefits are subtle but essential. Without it, you would never sure of the ability of the PC to perform its
tasks accurately and reliably.

Source: Evolution of Computers