ROM BIOS - Basic Input Output System - The BIOS is built-in software that determines what a computer can do without accessing programs from a disk. On PCs the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions. PnP features are built into modern BIOS chips.


EEPROM - (take a deep breath) Electrically Erasable Programmable Read Only Memory - Flash ROM. Read Only Memory that is able to be modified (reprogrammed) while remaining in the system.


Two basic form factors:

      

These may be socketed or soldered to MOBO

 

Memory use

  • The BIOS uses reserved memory locations from F0000h-FFFFFh (64K) but the fun starts at FFFF0h
  • Shadowing your BIOS – move the contents of the BIOS into RAM and run there
    • RAM is faster than ROM
    • Wider data path
    • Not as important anymore since Windows brings its own low-level drivers

 

BIOS manufacturers

  • Award – Phoenix
  • AMI

 

BIOS Main Features - Very A+

  • Bootstrap Loader
  • POST
  • Setup Program (CMOS)

BIOS programs – drivers that help the system deal with hardware devices

 

POST - Power On Self Test

One type of BIOS software, called the POST, helps test your computer each time you "power it on".

This software’s job is to "talk to" parts of the computer to find out if they are all working correctly.

  • Warm boot (ctrl-alt-del) no POST
  • The most noticeable POST tests are the memory, speaker and drive controller tests.
  • Not exhaustive but a good first line of defense.

Great for catastrophic mobo events.

 

Feedback: - Very A+

  • Audio - beep codes
    • AMI
    • Award BIOS
      • 1 long + 3 short = video error
      • Constant beeping = memory error
  • Alpha or numeric messages
    • 1XX errors: system board
    • 2XX errors: RAM or ROM
    • 3XX errors : k-board
    • 4XX, 5XX, 24XX: video adapter
    • 6XX: floppy
    • 17XX: HD controller
  • POST (diagnostic) Cards (monitor port 80h)

 

BOOTSTRAP LOADER

Bootstrap loader - a microcomputer's ROM BIOS chip contains instructions to search for the operating system, load it, and pass control to it.

"Bootstraps" help you get your boots on. Running the bootstrap loader, or booting the computer, helps the computer get its first instructions.

 

CMOS - battery-powered (rated in nano-amps) memory to hold the date, time, and system setup parameters. Usually located with the real-time clock in the motherboard chipset or in a separate real-time clock chip.

CMOS setup - allows editing of CMOS parameters. Keystroke roulette - Del, F1, F2, CTRL-ESC…

BIOS

Keystroke(s)

AMI

Del

Award

Del or Ctrl + Alt + Esc

Compaq

F1 or F10

Dell

Del or Ctrl + Alt + Enter

Gateway

F1

IBM

F1, Ctrl + Alt + Ins, or reference disk

Phoenix

F1, F2, Ctrl + Alt + S, or Ctrl + Alt +Esc

NEC

F1 or F10

 

Misc. CMOS Settings

A+ stuff - defaults, CPU, Port, floppy, hard drive, memory timings and parity, boot sequence, date/time, disabling virus check, disabling devices, power management, infrared, and passwords. Very A+

 

Interesting CMOS Settings

Plug and Play Aware O/S

When set to YES, BIOS will only initialize the PnP cards used for booting (VGA, IDE, SCSI). The rest of the cards will be initialized by the PnP operating system like Windows ® 98 or ME.

When set to NO, BIOS will initialize all the PnP cards.

Select Yes if the operating system is Plug & Play aware but does not use ACPI (advanced configuration power interface) to do it (Win2K or better).

 

Clear NVRAM or ESCD data

The ESCD (Extended System Configuration Data) NVRAM (Non-volatile Random Access Memory) is where the BIOS stores resource information for both PNP and non-PNP devices.

When this menu item is set to Yes, the system will reset ESCD NVRAM right after the system is booted up and then set the setting of the item back to No automatically.

If your system doesn’t have this option, move a PCI card to another slot. That sets up the same chain of events.

 

Password protecting your system
The CMOS setup password is stored in the CMOS memory area. This password set access to the CMOS setup program. On some notebooks it may in addition set access to the computer.


Clearing the CMOS

  • BIOS jumpers
  • Remove or short battery
    1. There are five different kinds of Real Time Clock CMOS chips (Dallas chips are an example) and they are all soldered in! The best strategy for these is to use the clear CMOS jumpers on the MOBO.
    2. For the Lithium battery follow these steps. First turn off the system, and then remove the lithium battery for a period of at least two hours. This should clear the CMOS setting and erase the password.
    3. Some motherboards use two solder points that you short with a flat head screwdriver. Others you should short the battery contacts after you remove the battery.

Software "killers" - KILLCMOS or BIOS killer

For the DOS elite - the following is a DEBUG command that works in DOS that can remove the BIOS password. Boot the computer with a DOS boot disk or and disk that has DEBUG.COM on it.

At the DOS prompt type, DEBUG. This will give you a prompt that looks like a dash. Type the following:

o 70 17
o 71 ff
q

Edited (2003) By Vlad Magero