Getting close to BIOS

BIOS :
Bios is a term that stands for the Basic Input / Output System. It consists of the low-level software that controls the system hardware and acts as a bridge between the OS and the hardware. In other words, BIOS is drivers.  BIOS is essentially the link between hardware and the software in a system. Here the software means the system software i.e. OS. The BIOS software containing all the device drivers for the entire system was collectively burned into one or more non-volatile ROM chips. It means that whenever the power was turned on the software in BIOS  is loaded in the RAM. The BIOS chip contains the power on self test (POST) program and a bootstrap loader. The bootstrap program was to initiate the loading of the OS and loading of the boot sector. After the completion it calls the on the low-level-routines in the BIOS to interact the system hardware. But in the modern PC when OS is loaded no more calls are made to any of the routines in the motherboard. They just load the device driver into RAM. This is why when the power is on the BIOS is mostly in ROM but after the OS is loaded the BIOS is entirely in RAM.
Basically, the combination of the motherboard BIOS, adaptercard BIOS device drivers loaded form the disks contributes the BIOS. The portion of the BIOS contained in the ROM chips is called firmware. The firmware is nothing but the name of the software which is stored on these chips.
BIOS hardware and software :
 The BIOS is a software running in memory that consists of all the various drivers that interface the hardware to the OS. The BIOS comes from the 3 possible sources :
  • Motherboard ROM
  • Adapter card ROM
  • Loaded into RAM from the disks

 The motherboard ROM BIOS is most associated with the hardware rather than software. It includes driver for all the basic system components with keyboard, hard drive, serial ports, latest video adapters, CD-ROM drives, SCSI hard disks, USB ports and many more.

A few adapters boards always have a ROM on board that includes :

  • Video cards
  • SCSI adapters
  • Network cards
  • IDE or floppy upgrade boards
  • Y2K boards

The setup program in the BIOS is used to set and store the configuration settings in the CMOS RAM.

Functions of BIOS :
Basically it has 4 main function :
  • POST ( Power On Self Test )
  • Setup
  • Bootstrap loader
  • BIOS

Don’t get confused with the 4th function of the BIOS is itself BIOS. This function refers to the collection of the actual drivers used to act as a basic interface between the OS and hardware when the system is booted and running.

Types of ROM chips :
There are 4 main types of ROM

  • ROM : Read Only Memory
  • PROM : Programmable ROM
  • EPROM : Erasable PROM
  • EEPROM : Electrically EPROM ( also called Flash ROM )

It does not matter what ROM the system uses, The data stored in a ROM chip is non-volatile and stays indefinitely unless erased or overwritten. 

To replace the BIOS chip, follow these steps :

  1. Back up the CMOS RAM settings.
  2. Power down the system and unplug the power cord.
  3. Remove the cover and any other components in the way of the BIOS EPROM chip. Remember to use caution with respect to static discharges; you should wear an antistatic wrist strap for this procedure or ground yourself to the chassis before touching any internal components.
  4. Using a chip puller or a thin flat-blade screwdriver, gently pry the chip out of its socket.
  5. Remove the new EPROM from the antistatic packing material in which it came.
  6. Install the new EPROM chip into the socket. A standard rectangular BIOS chip has a dimple atone end that corresponds to a cutout on the socket. You can install the chip in the socket back-ward, but if you do, you will destroy the chip.
  7. Reinstall anything you removed to gain access to the chip.
  8. Put the cover back on, plug in the system, and power on.
  9. Enter the BIOS setup information you saved earlier.
  10. Reboot and enjoy the new BIOS!
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