Introduction to the BIOSBIOS – Part 1

© Richard GoldmanRev. January 4, 2001

System BIOS

• BIOS = Basic Input/Output System• Interface between the hardware and the

Operating System of a computer• System BIOS is installed on the motherboard

and is system dependent.• Contained in a Read Only Memory (ROM) chip.• Note: Other hardware devices (adapter cards)

can also have their own BIOS.

RTC/NVRAMReal-Time Clock/Non-Volatile RAM

• Keeps the system time and date.• Stores the system configuration data.• Stores the Plug and Play settings shared by the

BIOS and the OS.

(ESCD – Extended System Configuration Data)

• Uses CMOS technology.(Complementary Metal-Oxide Semiconductor)

• CMOS memory is maintained and the system clock is powered by a lithium battery.

System BIOS

1. POST Program (Test and Configure)

2. Startup Routine (Bootstrap Loader)

3. Setup Program (System Configuration)

4. System BIOS (Hardware Drivers)

1. Time and Date2. System Configuration3. ESCD (PnP settings) (Extended System Configuration Data)

CMOS RAM (RTC/NVRAM)

Lithium Battery

System BIOS

The BIOS firmware contains:

• A setup program used to set and store system configuration information in the CMOS RAM.

• A Power On Self Test (POST) that tests the major components of the computer when it is first turned on.

• The startup program (the bootstrap loader) is used to locate and start the loading of the operating system.

• A collection of drivers that allows the operating system to communicate with the hardware.

System Layers

BIOS

DOS

Windows

Applications

Hardware

API Application Program Interface

Drivers

The BIOS Software

• Comes from:– Motherboard ROM BIOS– Adapter card ROM BIOS– Loaded form disk (hardware drivers)

• Software that is needed at startup needs to be located in a BIOS.

• The System BIOS will scan for and run other BIOS during startup.

• Common devices with their own BIOS:– Video, SCSI, NIC’s, Hard Drives, etc.

Types of ROM(Non-volatile RAM)

• ROM Read Only Memory• PROM Programmable ROM• EPROM Erasable PROM (UV erasable)• EEPROM Electronically-Erasable PROM

(Flash)

BIOS Manufacturers

• AMI – American Megatrends Inc.

• Award Software (now owned by Phoenix)

• Phoenix Software

BIOS Identification String

• Displayed in lower left corner of screen during startup.

• Unplug keyboard before turning on power to cause error and lock display so that you can view ID string.

• Obtain updated BIOS directly from Computer OEM (if available).

• Unicore and on-line sources such as hardwarehell.com are good sources for BIOS information and upgrades.