Thread: Motherboard Details

The motherboard is the main circuit board inside the Pc. It holds the processor, memory and expansion slots and connects directly or indirectly to every part of the Pc. It's made up of a chipset, some code in ROM and the various interconnections or buses. PC designs today use many different buses to link their various components. Wide, high-speed buses are difficult and expensive to produce: the signals travel at such a rate that even distances of just a few centimeters cause timing problems, while the metal tracks on the circuit board act as miniature radio antennae, transmitting electromagnetic noise that introduces interference with signals elsewhere in the system. For these reasOnS, PC design engineers try to keep the fastest buses 'confined to the smallest area of the motherboard and use slower, more robust buses, for other parts.

All motherboards include a small block of Read Only Memory (ROM) which is different from the main system memory used for loading and running software. The ROM contains the PC's Basic Input/ Output System (BIOS). This offers two advantages: the code and data in the ROM BIOS need not be reloaded each time the computer is started, and they cannot be corrupted by wayward applications that write into the wrong part of memory. A Flash upgradeable BIOS may be updated via a floppy diskette to ensure future compatibility with new chips, add-on cards, ete.
The BIOS comprises several separate routines, serving different functions. The first part runs as soon as the machine is powered on. It inspects the computer to determine what hardware is fitted and then conducts some simple tests to check that everything is functioning normally-a process called the power-on self test (POST). If any of the peripherals are plug and play devices, it's at this point that the BIOS assigns their resources.

There's also an option to enter the Setup program. This allows the user to tell the PC what hardware is fitted, but thanks to automatic self-configuring BIOSes this isn't used so much now. If all the tests are passed, the ROM then tries to determine which drive to boot the machine from. Most PCs ship with the BIOS set to check for the presence of an operating system in the floppy disk drive first (A, then on the primary hard disk drive. Any modern BIOS will allow the floppy drive to be moved down the list so as to reduce normal boot time by a few seconds. To accommodate PCs that ship with a bootable CD-ROM, some BIOSes allow the CD-ROM drive to be assigned as the boot drive. Some also allow booting from a hard disk drive other than the primary IDE drive. In this case, it would be possible to have different operating systems-or separate instances of the same OS- on different drives. Many BIOSes allow the start-up process to be interrupted to specify the first boot device without actually having to enter the BIOS setup utility itself.



If no bootable drive is detected, a message is displayed indicating that the system requires a system disk. Once the machine has booted, the BIOS serves a different purpose by presenting DOS with a standardized API for the PC hardware. In the days before Windows, this was a vital function, but 32-bit "protect mode" software doesn't use the BIOS, so again it's of less benefit today. Windows 98 (and later) provides multiple display support. Since most PCs have only a single AGP slot, users wishing to take advantage of this will generally install a second graphics card in a PCI slot. In such cases, most BIOSes will treat the PCI card as the main graphics card by default. Some, however, allow either the AGP card or the PCI card to be designated as the primary graphics card. Whilst the PCI interface has helped - by allowing IRQs (Interrupt ReQuest: a signal generated by a device to request processing time from the CPU. Each time a keyboard button is pressed or a character is printed to a screen, an IRQ is generated by the requesting device. IRQ signals are transmitted along IRQ lines, which connect peripheral devices to a programmable interrupt controller, or PIC.

A PC has 16 IRQs, and no two operational devices can share the same IRQ to be shared more easily, the limited number of IRQ settings available to a PC, remains a problem for many users. For this reason, most BIOSes allow ports that are not in use to be disabled. With the increasing popularity of cable and ADSL Internet connections and the ever-increasing availability of peripherals that use the USB interface, it will often be possible to get by without needing either a serial or a parallel port. Motherboards are multiple layer printed circuit boards, also sometimes called PCBs. The' physical board that you see is actually a combination of several thinner layers, each containing some of the circuitry required to connect the various components on the board. At one time this was expensive, difficult-to manufacture technology, but progress in technology has reduced this complexity. till, good motherboards are reliable and well designed, while cheaper ones tend to be fragile, and Increase the chance of a electrical problem on the board. In addition, better boards reduce interference problems because of their design, and reduce the chances of problems in assembling the Pc. Thin boards are more subject to damage from flexing when In erting peripherals; the thicker the board, the better.