BIOS (OCR A Level Computer Science)
Revision Note
Written by: Callum Davies
Reviewed by: James Woodhouse
BIOS
What does BIOS mean?
BIOS stands for Basic Input/Output System
BIOS is a piece of firmware stored on a small memory chip on the motherboard
On system start, the BIOS is the first software to run
It performs a POST (Power-On Self-Test), a diagnostic testing sequence that ensures all the hardware components are working properly
If the BIOS encounters any errors during this test, it will either halt the boot process or issue an error message
If the POST succeeds, the BIOS will run the Bootstrap loading sequence, which is the program responsible for starting the operating system
Worked Example
In the late 1990s, the CIH virus hit the headlines because it could overwrite and destroy the contents of a computer’s BIOS.
Describe the effect of a computer having its BIOS overwritten.
[2]
How to answer this question:
Explain the role of BIOS in a computer system
Explain the consequence of having a destroyed BIOS
Answer:
Example answer that gets full marks:
The BIOS is crucial in initialising the hardware components and operating the system. If a virus, such as the CIH virus, overwrites or destroys the contents of a computer's BIOS, it will be unable to perform the Power-On Self-Test (POST) and fail to load the bootstrap program. This would mean the computer will not be able to initialise the operating system.
Acceptable answers you could have given instead:
If the BIOS has been overwritten, it will not be able to perform the Power-On Self-Test (POST) and, therefore, unable to load the bootstrap program. This would mean the operating system would fail to start.
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