- 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.
- POST ( Power On Self Test )
- Bootstrap loader
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 :
- Back up the CMOS RAM settings.
- Power down the system and unplug the power cord.
- 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.
- Using a chip puller or a thin flat-blade screwdriver, gently pry the chip out of its socket.
- Remove the new EPROM from the antistatic packing material in which it came.
- 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.
- Reinstall anything you removed to gain access to the chip.
- Put the cover back on, plug in the system, and power on.
- Enter the BIOS setup information you saved earlier.
- Reboot and enjoy the new BIOS!
File infector virus: Most common form of the computer virus is the file infector virus, that hides its code within the code of the another programs. Its an executable program typically with exe, bat, pif, sys or com extension. By loading itself to the memory it runs separately and even can continue if the host program is closed. This type of virus is responsible for 85% of the infections.
Boot sector virus : It resides in the part of the hard disk which is read in the memory when the computer firsts boot up. since removable disks are less used today, boot sector viruses have become much less prevalent than they used to be.
- Creation : Virus is created.
- Replication : Virus is copied from pc to pc.
- Activation : Virus launches and delivers destructive payloads.
- Discovery: Virus is detected and documented.
- Assimilation : Anti-viruses companies modify their programs to include new virus.
- Eradication : Use of anti-virus removes the threats.