PC Troubleshooting FAQ
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Introduction to the
The term BIOS is typically used to refer
to the system BIOS, however, various other components such as video
adapters and hard drives can have their own BIOSes hardwired to them.
During the rest of this section, we will be discussing the system BIOS.
The BIOS software lives on a ROM IC on the motherboard known as a
Complementary Metal Oxide Semiconductor(CMOS). People often incorrectly
refer to the BIOS setup utility as CMOS, however, CMOS is the name of
the physical location that the BIOS settings are stored in.
|Software Layer Model
||BIOS stands for Basic
Input/Output System and is software that manages hardware and
allows the operating system to talk to the various components.
The BIOS is also responsible for allowing you to control your
computer's hardware settings, for booting up the machine when
you turn on the power or hit the reset button and various other
Basic CMOS Settings:
BIOS services are accessed using software interrupts, which are similar
to the hardware interrupts except that they are generated inside the
processor by programs instead of being generated outside the processor
by hardware devices.
- Printer Parallel Port
- Unidirectional - Single direction communication.
- Bi-directional - Two directional communication. Used by HP
- ECP(Extended Capability Port) - Same as Bi-directional but
uses a DMA to bypass processor and speed up transfer.
- EPP(Enhanced Parallel Port) - Same as bi-directional and
offers an extended control code set.
- COM/Serial Port
- Memory Address - Each COM port requires a unique memory
- IRQ - Every COM port requires a unique IRQ to talk to the CPU.
- COM1 = IRQ4 and 03F8
- COM2 = IRQ3 and 02F8
- Hard Drives
- Size - The Size is automatically detected by the computer.
- Primary Master/Secondary Slave
- Each hard drive has a controller built in the drive that
controls the drive.
- If two drives were on the same channel the adapter could get
- By setting one as a master it tells it which is in charge.
BIOS routines begin when the computer is booted and are mad up of 3 main
operations. Processor manufacturers program processors to always look in
the same place in the system BIOS ROM for the start of the BIOS boot
program. This is normally located at FFFF0h - right at the end of the
First, the Power On Self Tests(POST) are conducted. These tests verify
that the system is operating correctly and will display an error message
and/or output a series of beeps known as beep codes depending on the
Second, is initialization in which the BIOS looks for the video card. In
particular, it looks for the video card's built in BIOS program and runs
it. The BIOS then looks for other devices' ROMs to see if any of them
have BIOSes and they are executed as well.
Third, is to initiate the boot process. The BIOS looks for boot
information that is contained in file called the master boot record(MBR)
at the first sector on the disk. If it is searching a floppy disk, it
looks at the same address on the floppy disk for a volume boot sector.
Once an acceptable boot record is found the operating system is loaded
which takes over control of the computer.
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