MOTHERBOARD

Difference between AT and ATX:
AT and ATX are different form factors for Computers. A form factor is the physical layout of the motherboard and its associated case. Changing the design of a motherboard usually means changing the design of the case.
There are different variations on the AT design. There is the original AT, and the Baby AT form factor. The Baby AT design is simply a smaller version of the original AT design. It is therefore less expensive to make. A Baby AT motherboard can usually fit inside either a Baby AT case or a full AT case. However, an AT motherboard is too big to fit in a Baby AT case and it therefore must fit into an AT case only.
The ATX is a newer design for motherboards and cases. The ATX design uses a different power supply connector and the ATX case cools internal components much more efficiently than its predecessor. In addition to ATX, there is also Mini ATX and Micro ATX. These are smaller versions of the ATX motherboards and cases which adhere to the ATX design specifications, but skimp on expandability.

MotherBoard Architecture

1. Slot 1 Connector - this is where your Pentium II or Pentium III processor fits in. If you are using a standard Pentium, AMD K5 or K6, a WinChip or an IBM/Cyrix processor then you will be using a Socket 7 (sometimes called Super 7 for the newer chips) motherboard and the connector will be as shown under the main diagram.
2.ISA (Industry Standard Architecture) Expansion Slots - used to add expansion cards such as sound cards and internal modems. This type of expansion slot has a 16-bit bandwidth with a frequency of 8MHz. They are the older interface and are now being phased out.
3.PCI (Peripheral Component Interface) Slots - these are a newer type of expansion slot than the ISA ones and more components are now making use of them instead of the older slots. They have a 16-bit bandwidth and a frequency of 33MHz.
4. AGP (Accelerated Graphics Port) - these are the newest standard in expansion slots, for use only with graphics boards. The newer model has a 64-bit bandwidth and a frequency of 66MHz.
5. Memory Slots - the ones shown are DIMM (Dual Inline Memory Module) slots. Used to add memory to your computer.
6. Jumpers - these are used to configure the options on your motherboard, such as processor voltages etc. The jumper is placed over two pins to cause an electrical connection. Your motherboard manual should tell you the settings for each jumper.
7.Floppy disk and Primary/Secondary IDE channels - used to interface you hard drives, CD-ROMS and floppy drives to your motherboard. The smaller connector is for the floppy drive, and the two larger ones are for IDE (Integrated Drive Electronics) devices such as hard drives and CD-ROM drives. Up to two devices can be used from one channel, so on this motherboard you could have up to two floppy drives with four IDE devices.
8. Front Panel Connectors - these connect to the lights on the front of your system case to notify you of hard disk access, power etc. If you have an ATX style case then a power connector also fits here. The wires that should be connected to these come from the front of the case.
9. Real-Time Clock battery - allows the computer to retain the time when it is powered down. Also retains configuration data from when you first set up your computer.
10. BIOS EEPROM (Basic Input-Output System Electrically Erasable Programmable Read-Only Memory) - The BIOS configures the system resources on your system, and performs the self-check procedure each time you switch on your PC.
11. Ports - connects external peripherals to the system such as a keyboard, mouse and printer. Most modern systems will have one each of PS/2 keyboard and mouse connectors, two serial ports, one parallel port and two Universal Serial Bus (USB) ports.

12. Voltage Regulation - these components help to regulate the power supply to prevent 'spikes' when the power is switched on.

13. Power Supply Connector - this is where the power arrives from your case's PSU (Power Supply Unit). The one shown on this board is an ATX style connector and supports extra features such as auto shut-down and energy saving compatibility. The older AT style connectors have only a single row of pins and don't support these extra features.

Motherboard

A computer motherboard is the most important part of a computer.
It is the main printed circuit board (PCB) in the computer and is sometimes referred to as the system board or mainboard.
The motherboard itself is just a piece of fiberglass. It's actually the hardware mounted on it that does all the work in the computer.
The motherboard connects directly or indirectly to every other part of the computer.
Its dimensions vary with the size of the system for which it was made. There are fine copper traces etched onto the board which forms the bus.
The bus carries power and information between the components on the motherboard.
Numerous tiny holes are drilled in the bus on the motherboard into which chips, sockets and other electronic components are installed.
These electronic components are held in place by soldered joints on the underside of the board.
There are also other holes drilled into the motherboard to accept spacers and screws for securing the motherboard to the case.
The evolution of the motherboard has caused more devices to be integrated into the motherboard.



Typical Motherboard Diagram
The parts of the computer motherboard such as RAM and CPU that are more subject to change, have been integrated into sockets so that they can be easily removed and replaced for upgrading.
You will encounter many different types and sizes of motherboards which will be determined by its form factor.
The form factor determines the size and shape of the mainboard and also dictates what kind of case it will fit into.
Listed below are the different types of form factors.
PC/XT - Although it wasn't the first PC, it had many features that were not available with previous PC designs. One such feature was that it was the first computer to have a hard drive.
It also had a large computer motherboard that was installed into a full size horizontal or desktop case.
Full-Size AT - The full-size AT mainboards were large in order to accommodate a lot of circuitry and could be installed in full-size AT desktop and tower cases. At present, full-size AT motherboards are no longer produced.
Baby-AT - Between 1983 to 1986, Baby-AT form factor became the most popular computer motherboard because it was able to fit into a number of different case designs. Today, you may still be able to get motherboards of this design.
In 1996, the Baby-AT was replaced by the ATX design.
LPX - This board was a semi-proprietary motherboard design which was difficult to repair and upgrade. Also, replacement parts for upgrades were expensive thus making it more economical to purchase a brand new non-proprietary design.
ATX - This design improved upon the Baby-AT and the LPX designs. Its physical dimensions are approximaely 12" x 9.6". This design is not compatible with AT designs because the motherboard is turned sideways in the case and has a different power supply connector.
Micro ATX - This is a smaller version of the ATX form factor. Its physical dimensions are approximately 9.6" x 9.6".
All form factors that precede the ATX are now obsolete. A new form factor called BTX is now emerging. There will be three basic sizes:
picoBTX - 7.9" x 10.4".
microBTX - 10.3" x 10.4".
BTX - 12.7" x 10.4".
NOTE: Today, the ATX is the most popular design of the newer motherboards and it is easily upgradeable.
Computer motherboard designs are constantly changing. Listed below are the major components of the motherboard:
BIOS:
Another important component is the basic input/output system (BIOS) chip which contains startup programs such as the power on/self-test (POST) and drivers of the computer.
This chip controls communication between the systems hardware and operating system. BIOS can also be referred to as firmware.
Expansion Slots:
Expansion slots enable the CPU to communicate with the peripheral devices which expand the capability of the computer.
Different cards can be plugged into these slots to enhance the computer such as video cards to improve graphics and sound cards to provide better audio.
Battery:
This battery is referred to as CMOS battery and is responsible for keeping the time and date. It usually has a life span of about 3 to 4 years.
Memory:
In a computer system, the CPU needs information and instructions to perform properly. This information and instructions for the CPU are stored in Random Access Memory (RAM). This memory is sometimes referred to as Primary Memory or Main Memory.
Ports:
Ports allow external devices to be connected to the computer motherboard. There are different types of ports located on the motherboard such as parallel, serial, universal serial bus (USB) and SCSI (small computer system interface).
Until up to a few years ago, printers were connected to parallel ports but now they are being replaced with the faster USB port. Low speed peripherals such as modems, mice and some scanners were connected to the serial port.
Again, this port is being replaced by the USB port which can support up to 127 devices. The SCSI bus can also support a number of peripherals such as hard disks, tape drives, CD-ROM drives, scanners, etc.
Power Connector:
This is a 20-pin male connector located on the computer motherboard. The power supply is plugged into this connector which supplies power for the motherboard, its components and some peripherals.
Most new motherboards now come with a 24-pin connector. Older motherboards with 20-pin connectors can still be used with a 24-pin power supply since this 24-pin connector can be separated into 20-pin and 4-pin connectors.
Integrated Graphics and Audio:
Today, most of the motherboards manufactured include integrated graphics, audio and LAN.
Hard Drive Data Transfer Modes-(Interface):
Motherboards are designed to provide different data transfer rates. First time computers used the UDMA/33 interface but this was increased to UDMA/66 which doubled the data-transfer rate.
The data transfer rate of a hard drive is the time used to read/write information. This interface mode was upgraded to UDMA/100 and then finally to UDMA/133.
These characteristics apply to Parallel ATA hard drives. For a long time, the UDMA/133 remained the fastest interface until the inception of the Serial ATA drive which has a data transfer rate of 150MBS/sec. These have now improved to data transfer rates of 300MBS/sec.
These hard drives can be operated in different modes called RAID (Redundant Array of Independent Disks). RAID requires more than one hard drive.
This provides speed by writing/reading information to more than one drive simultaneously - called 'striping' (RAID, 0).
Another feature is data security or 'mirroring' which duplicates data on both hard drives (RAID,1).