Bootstrapping Using The BIOS
Motherboards contain some non-volatile memory to initialize the system and load an operating system from some external peripheral device. Microcomputers such as the Apple II and IBM PC used ROM chips, mounted in sockets on the motherboard. At power-up, the central processor would load its program counter with the address of the boot ROM and start executing ROM instructions. These instructions displayed system information on the screen, ran memory checks, and then loaded an operating system from an external or peripheral device (disk drive). If none was available, then the computer would perform tasks from other memory stores or display an error message, depending on the model and design of the computer and version of the BIOS.
Most modern motherboard designs use a BIOS, stored in an EEPROM chip soldered or socketed to the motherboard, to bootstrap an operating system. When power is first applied to the motherboard, the BIOS firmware tests and configures memory, circuitry, and peripherals. This Power-On Self Test (POST) may include testing some of the following things:
- Video adapter
- Cards inserted into slots, such as conventional PCI
- Floppy drive
- Thermistors, voltages, and fan speeds for hardware monitoring
- CMOS used to store BIOS setup configuration
- keyboard and mouse
- network controller
- Optical drives: CD-ROM or DVD-ROM
- SCSI hard drive
- IDE, EIDE, or SATA hard disk
- Security devices, such as a fingerprint reader or the state of a latch switch to detect intrusion
- USB devices, such as a memory storage device
On recent motherboards, the BIOS may also patch the central processor microcode if the BIOS detects that the installed CPU is one in for which errata has been published.
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