Motherboard, BIOS and POST

1. Motherboard, BIOS and POST • The 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 devices • But with what software does the CPU use to communicate with these devices?

2. BIOS! • Bios is software that contains hundreds of programs that allow for communication between the CPU and devices • Bios is stored on ROM, which is a permanent chip on the motherboard • Bios is software, ROM is hardware

3. Three kinds of BIOS software for Hardware devices • Permanent never changing BIOS for permanent hardware • stored on the ROM chip • example-keyboard • Hardware that changes occasionally • requires extra volatile information so it must be stored on a separate chip called the CMOS • example- RAM, hard drives, floppy drive • The other devices- 2 options • BIOS is stored on the devices(example-sound card) • or device drivers are installed to ensure communication between CPU and device

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

5. CMOS for the Devices that can change • CMOS- Complimentary metal-oxide semiconductor • Stores information that is updated • Also acts as a clock to keep time and date • Enter CMOS by pressing F1 or some other combination of keys • Powered by separate 3 volt battery, usually a lithium rechargable

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

7. A Quick Word on the Registry • The registry, which first came with Windows 95, replaced config.sys, system.ini along with other ini files found in DOS and Windows 3x • If you need to edit the registry you run the command regedit.exe • HOWEVER!, you usually don’t need to. You have Control Panel to most of the changes you will ever need to make

8. POST- Power On Self Test • Stored on the ROM chip • Runs every time computer is turned on • Instructs all devices to run a self check to determine if everything is working • First the basic devices checked and beeps are sounded to indicate problems • Second the rest of the devices are run and error codes are displayed to indicate problems

9. POST cards- to check up on faulty POST • POST 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 on • Having this card can get you out of an endless loop, where the POST test prevents you from continuing on

10. The Boot Process • 1st- When you press the power on switch the CPU is “awakened” by a charge of electricity. • 2nd- The POST is run • 3rd-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

11. The Boot Process Continued • 5th- 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 disk’s “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 from • 7th-The Operating System takes control!

12. Motherboard Layouts • The way components are positioned on the motherboard is called the motherboard’s form factor • There are two types: AT and ATX • AT older uses the P8 and P9’s • other version called Baby AT which was smaller • ATX newer uses the P1 power connector

13. Replacing a Motherboard • Step by step instructions: