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What is BIOS of a Computer?

Introduction to BIOS

In today's video our topic is 'BIOS and UEFI Legacy'.

BIOS is a chipset which is already installed on our computer's motherboard. It is a personal operating system of motherboard. BIOS is nothing but Basic Input Output System. If BIOS is not present in our system, our system will not at all work properly. It is mainly responsible for booting our system.

- BIOS stands for Basic Input Output System.
- BIOS is the instructions used to start the computer from a cold start. (power off to power on).
- The BIOS instructions are written on non-volatile RAM.
- EEP-ROM is the common media choice for the BIOS, installed on the motherboard.
- The BIOS instructions are based on the chip-set installed on the motherboard.
- In simple language BIOS is personal Operating System for our Motherboard, no component like RAM, Graphic card & others will start with this.
- Understanding the concept of BIOS is very important because sometime any component which is fitted in our motherboard starts showing problem, so to troubleshoot that problem mainly BIOS concepts are used.

BIOS Primary Functions :
- It issues the Instructions for starting the Hardware at boot time.
- Load the OS from the boot device.
- Also, BIOS setup utility helps to see some statistics about our Hardware & CPU.

Interfaces of every different BIOS are not at all same. We'll further see that what are the Advanced BIOS utility features.

F10 key is used to Save and Exit while ESC key is use toh Exit directly without saving in the BIOS Setup.

How Hardware Boot System for BIOS works are mentioned below stepwise :
-Turn on the power switch.
- All memory and cache is empty at startup.
- A reset signal is generated by the chipset to the CPU until the power is ready.
- The CPU powers up and reads address xFFFFO from the ROM. This contains a jump instruction to the start of the BIOS instructions.
- Video and keyboard are activated early in the boot sequence (video start instruction in ROM address is xC000)
- Other devices are activated like the disk drives, optical drives, sound-card, NIC, USB bus, etc.
- BIOS setup becomes available for the user.
- Following is the sequence how boot ROM & boot Loader works :
Power ON --> Primary Boot Loader --> Secondary Boot Loader --> Hardware Init / Modem Image Execution / Kernel Image download and Execution

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