The Setup programs
There are three elements in the start-up part of the
You may follow the checks being executed in this order, as the information are gathered:
POST also reads those user data, which are found in the CMOS. This is discussed in the following chapter.
The DOS Boot Record (DBR) also holds a media descriptor as well as information on the OS version. Please read module 6a4 on this issue. You can use DiskEdit (included in the "Norton Utilities") to read view the contents of the boot sector.
When the disk holds no boot strap routine, you get an error message like "Non-system disk, replace with system disk and press any key".
CMOS is only a medium for storage. It could be used for any type of data. Here, it holds important system data, values to be used during the start process. These information take up maybe 100 or 200 bytes of data, and storage in the CMOS makes them instantly available to the POST and BIOS programs (loaded from ROM) during the start-up.
The values are regarding:
These data have to be set up correctly, and they are read during the start-up to make the PC operable.
For example, POST cannot by itself find sufficient information about the floppy drive(s). Floppy drives are so "dumb," that POST cannot read whether they are floppy drives or not, nor what type. About the same goes for IDE hard disks, while EIDE hard disks are a little more "intelligent," However, POST still needs assistance to identify them 100% correctly.
The same goes for RAM: POST can count how much RAM is in the PC. However, POST cannot always detect whether it is FPM, EDO or SD RAM. Since the CPU and BIOS reads data from RAM chips differently, depending on the RAM type, the type must be identified to setup the correct timing.
Other data in CMOS contain various user options . This is data, which you can write to CMOS. For example, you can adjust date and time, which the PC then adjusts every second. You can also choose between different system parameters. Maybe you want a short system check instead of a long one. Or if you want the PC to try to boot from hard disk C before trying floppy disk A, or vice versa. These options can be written to CMOS.
Many of the options are of no interest to the ordinary user. These are options, which regard controller chips on the motherboard, which can be configured in different ways. Ordinarily, there is no need to make such changes. The motherboard manufacturer has already selected the optimal configurations. They recommend in their manuals, that you do not change these default settings.
We can conclude, that CMOS data are essential system data, which are vital for operation of the PC. Their special feature is, that they are user adjustable. Adjustments to CMOS are made during start-up.
Opening the Setup program
You communicate with the BIOS programs and the CMOS memory through the so-called Setup program. This gives us a very simple user interface to configuring the PC with these vital data.
Typically you reach the Setup program by pressing [Delete] immediately after you power up the PC. That brings you to a choice of setup menus. You leave Setup by pressing [Esc], and choose "Y" to restart the PC with the new settings. Generally, you should not change these settings, unless you know precisely what you are doing.
Here you see the start menu of the American Megatrends BIOS Setup program, which has a kind of graphical user interface. You are supposed to use the mouse:
Read more about the boot process and system bus in Module 2b
Read more about I/O buses in module 2c
Read more about the motherboard chip set in module 2d
Read more about RAM in module 2e
Read about EIDE in module 5b
I also recommend two books for further studies. Gunnar Forst: "PC Principals", from MIT is excellent. Also "The Winn L. Rosch Hardware Bible" from Brady covers the same subjects. Also "PC Intern" from Abacus is fine.
Links to BIOS information:
Mr BIOS FAQ
Copyright (c) 1996-2005 by Michael B. Karbo. www.karbosguide.com.