Motherboard, BIOS and POSTThe external data bus connects devices on the motherboard together. Everything is also connected to the address bus. These busses are the physical connections between the devicesBut with what software does the CPU use to communicate with these devices?

BIOS!Bios is software that contains hundreds of programs that allow for communication between the CPU and devicesBios is stored on ROM, which is a permanent chip on the motherboardBios is software, ROM is hardware

Three kinds of BIOS software for Hardware devicesPermanent never changing BIOS for permanent hardwarestored on the ROM chipexample-keyboardHardware that changes occasionallyrequires extra volatile information so it must be stored on a separate chip called the CMOSexample- RAM, hard drives, floppy driveThe other devices- 2 optionsBIOS is stored on the devices(example-sound card)or device drivers are installed to ensure communication between CPU and device

First Group the PermanentsThis BIOS is called firmware, since it is software that does not changeIt is stored on nonvolatile memory called a ROM chip (Read Only Memory)The Newer Flash ROM enables users to change this ROMPhoenix and AMI are most common brands

CMOS for the Devices that can changeCMOS- Complimentary metal-oxide semiconductorStores information that is updatedAlso acts as a clock to keep time and dateEnter CMOS by pressing F1 or some other combination of keysPowered by separate 3 volt battery, usually a lithium rechargable

Third kind of BIOS: BIOS is on the device or comes with device driversIf your BIOS does not support a device, you must add a device driver, which usually comes on a disk with the deviceFor DOS programs you can use Config.sys to add the BIOSFor Window 3x you can also use system.iniFor Windows 95/98 drivers are automaticly stored in the Registry.

A Quick Word on the RegistryThe registry, which first came with Windows 95, replaced config.sys, system.ini along with other ini files found in DOS and Windows 3xIf you need to edit the registry you run the command regedit.exeHOWEVER!, you usually dont need to. You have Control Panel to most of the changes you will ever need to make

POST- Power On Self TestStored on the ROM chipRuns every time computer is turned onInstructs all devices to run a self check to determine if everything is workingFirst the basic devices checked and beeps are sounded to indicate problemsSecond the rest of the devices are run and error codes are displayed to indicate problems

POST cards- to check up on faulty POSTPOST cards can be used to check up on a problem that the POST check has detected or caused. The card is inserted into an expansion slot, and then the computer is turned onHaving this card can get you out of an endless loop, where the POST test prevents you from continuing on

The Boot Process1st- When you press the power on switch the CPU is awakened by a charge of electricity.2nd- The POST is run3rd-Errors are checked for and the screen displays. After the screen is displayed other devices are checked and an error message displays is something is wrong

The Boot Process Continued5th- Plug and play devices are searched for and configured if needed. A brief summary of devices is displayed on screen.6th-BIOS then begins its search for the operation system. It looks on the disks boot sector to see where the operating system is on the disk. In most computers the BIOS looks for the floppy drive first to boot from7th-The Operating System takes control!

Motherboard LayoutsThe way components are positioned on the motherboard is called the motherboards form factorThere are two types: AT and ATXAT older uses the P8 and P9sother version called Baby AT which was smallerATX newer uses the P1 power connector

Replacing a MotherboardStep by step instructions: