Contributed By:- Divyanshu Pathania
GNDU RC SATHIALA
The term BIOS was coined by Gary Kildall and was used to
describe the machine-specific part loaded during boot time that interfaces
directly with the hardware. Today, the fundamental purpose is to initialize and
test the system hardware components and to load a boot loader or an operating
system from a mass memory device. The BIOS additionally
provides abstraction layer for the hardware, i.e. a consistent way for
application programs and operating systems to interact with the keyboard,
display, and other input/output devices. Variations in the system hardware are
hidden by the BIOS from programs that use BIOS services instead of directly
accessing the hardware. Modern operating systems ignore the abstraction layer
provided by the BIOS and access the hardware components directly.
Basically,
it contains instructions that are set and stored on the motherboard of a C.P.U.
and can work on any computer.
In
modern computer systems, the BIOS contents are stored on a flash
memory chip so that the contents can be rewritten without removing
the chip from the motherboard. This allows BIOS software to be easily upgraded
to add new features or fix bugs, but can make the computer vulnerable to BIOS root kits.
These
programs and instructions remain in the PC throughout its lifetime and usually
these instructions cannot be altered. But we can upgrade/replace them as and
when needed.
Basically
these instructions, also sometimes known as ROM Code hold various start-up
instructions for our system.
These
instructions/programs can be summarised in the following keywords:
1.
POST (POWER ON SELF TEST): It is a set of instructions that
is connected to various hardware peripherals. In fact, it is
a process performed by firmware or software routines immediately after many digital electronic devices are powered
on. The power-on self-test tests, identifies, and initializes system
devices such as the CPU, RAM, interrupt and DMA controllers and other parts of the chipset, video display card, keyboard, hard disk drive, optical disc drive and other basic hardware.
The BIOS then locates boot loader software held on a storage device designated as a 'boot device', such as
a hard disk, a floppy disk, CD, or DVD, and loads and executes that software,
giving it control of the PC.[8] This process is known as booting, or booting up, which is short for "bootstrapping".
2.
BOOT INSTRUCTIONS: which call the operating system (for
example: windows)
3.
Versions of MS DOS contain a basic file called as
"IO.SYS", "COMMAND .COM" or "DRBIOS.SYS". This
file is the "DOS BIOS" (aka "DOS I/O System") and contains
the lower-level hardware-specific part of the system.
4.
BIOS boot process: When the x86 processor is reset, it loads its program counter with a fixed address near the top of the 1
megabyte real-mode address space. The BIOS ROM chip is located in
memory so that its starting address is within the BIOS. A jump instruction redirects
the processor to start executing the code in the BIOS.
5.
COLD BOOT- If
the system has just been powered up or the reset button is pressed ("cold
boot"), the full power-on self-test (POST) is run. If ctrl+alt+delete
combination is initiated ("warm boot"), a special flag value is
detected in non volatile memory (NVRAM) and the BIOS does not run the POST.
This saves the time otherwise used to detect and test all memory. The NVRAM is
in the real-time clock (RTC).
It
is important to note that BIOS is sensitive to static charge, therefore proper
care must be taken while handling it. Sometimes BIOS can be password protected
as well, but never forget this password. Once lost, it is very difficult to
recover the BIOS password.
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