Advanced BIOS

·       BIOS contains basic instructions for communication between the cpu and I/O devices

·       BIOS in older machines, such as 286, 386 and 486, have a limited number of hard drive settings to choose from, and do not have an auto select feature.

·       The BIOS is located in ROM between F0000 and FFFFF

·       The POST program starts in the ROM at the memory address F000

·       During system operation, the BIOS controls all low level communication between the operating system and the hardware.

·       Shadowing – process of loading the contents of the BIOS from ROM into faster RAM

·       Flash ROM – allows the BIOS to be upgraded without removing the ROM chip

·       Boot process:

1.     BIOS àPost

2.     CMOS is accessed

3.     BIOS opens the File Allocation Table (FAT) located on the MBR of the hard drive

4.     IO.SYS called on by BIOS

5.     CONFIG.SYS called on by IO.SYS

6.     MSDOS.SYS called on by BIOS

7.     COMMAND.COM called on by BIOS

8.     AUTOEXEC.BAT called on by MSDOS.SYS

CMOS

·       You should record the data in CMOS before disassembling a computer

·       CMOS must be set if setting up a computer for the first time, or after adding new components.

·       CMOS does not contain any programs, it only holds configuration data

·       To properly setup a hard drive in CMOS, the following information must be entered:

o      Capacity

o      Cylinders

o      Sectors

CMOS Problems

·       If CMOS contains a password that you don’t know, you can usually clear it, and everything else in CMOS, by shorting the Clear CMOS jumper located on the motherboard.