Basic Hardware Notes -

THE MOTHER BOARD
The motherboard is the main circuit board inside the PC which 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 (known as the ‘glue logic’), 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


BAT
to a typical 9in wide by 10in long, and BAT motherboards are generally characterized by their shape, an AT-style keyboard connector soldered to the board and serial and parallel port connectors which are attached using cables between the physical ports mounted on the system case and corresponding connectors located on the motherboard. With the BAT design the processor socket is located at the front of the motherboard, and full-length expansion cards are intended to extend over it. AT power supplies only provide 12V and 5V outputs to the motherboard, requiring additional regulators on the motherboard if 3.3V components (PCI cards or CPUs) are used.
ATX
The Intel Advanced/ML motherboard, launched in 1996, was designed to solve these issues and marked the beginning of a new era in motherboard design. Its size and layout are completely different to the BAT format, following a new scheme known as ATX. The dimensions of a standard ATX board are 12in wide by 9.6in long; the mini ATX variant is typically of the order 11.2in by 8.2in. The ATX uses a new specification of power supply that can be powered on or off by a signal from the motherboard. This allows notebook-style power management and software-controlled shutdown and power-up. A 3.3V output is also provided directly from the power supply. Mini-ATX is simply a smaller version of a full-sized ATX board. On both designs, parallel, serial, PS/2 keyboard and mouse ports are located on a double-height I/O shield at the rear.
MicroATX
Introduced in the late 1990s, the MicroATX is basically a smaller version of Intel's ATX specification, intended for compact, low-cost consumer systems with limited expansion potential.
The maximum size of the board is 9.6in square, and it’s designed to fit into either a standard ATX case or one of the new micro-tower desktop designs.
FlexATX
The Flex ATX is a natural evolution of the Intel's micro ATX form factor which was first unveiled in late 1999. The Flex ATX addendum to the micro ATX specification addresses the requirements of only the motherboard and not the overall system solution. As such, it does not detail the interfaces, memory or graphics technologies required to develop a successful product design
The principal difference between FlexATX and microATX is that the new form factor reduces the size of the motherboard - to 9in x 7.5in. Not only does this result in lower overall system costs, it also facilitates smaller system designs
BIOS
All motherboards include a small block of Read Only Memory (ROM) which is separate 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 etc.
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 BIOS this isn’t used so much now. Most PCs ship with the BIOS set to check for the presence of an operating system in the floppy disk drive first, 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 BIOS 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.
CMOS-RAM
Motherboards also include a separate block of memory made from very low power consumption CMOS (complementary metal oxide silicon) RAM chips, which is kept ‘alive’ by a battery even when the PC’s power is off. This is used to store basic information about the PC’s configuration: number and type of hard and floppy drives, how much memory, what kind and so on. All this used to be entered manually, but modern auto-configuring BIOSes do much of this work, in which case the more important settings are advanced settings such as DRAM timings.