Typical motherboard hardware characteristics

Hardware components of the PC
The System Board
Typical motherboard hardware characteristics

The diagram of the ATX motherboard below shows several of the important parts. The processor connection towards the right hand side of the photograph is called a Slot One connection, which will take a Pentium II or Celeron Processor. The Pentium II processor is mounted on a small daughter board that has integral level 2 cache memory on board.

The size and layout of the motherboard has changed over the years as new technology has appeared, but most of the evolution has taken place since 1995. Some items such as memory and processors have remained in sockets, but other additions such as graphics, sound, SCSI and network have been incorporated on to the motherboard, so that additional cards are not required. The motherboards have divided themselves into AT and ATX type boards, which identify themselves by the type of power supply and connector they use. There are some motherboards that have both power supply connectors on them. The main difference between AT and ATX motherboards is the way they are switched on and the power management available:

AT - This type of motherboard has been around since the first ATs were built by IBM. They have a normal mains switch that switches the mains supply and generally the power management they have is just switching off the monitor.
ATX - This type of power supply places the mains power switch physically on the power supply. Once switched on the motherboard remains in standby, ready to come to life by the pressing of a small push to make switch, a password entered at the keyboard or a key combination, such as [Ctrl] and [F1]. Some motherboards have an LED that remains alight when the mains power switch is on but the motherboard is in standby. The ATX power supply and motherboard combination will also give more power management that will switch off automatically when the operating system is closed down and goes into standby after a period of time determined by the Advanced Power Management (APM) of the operating system.

The diagrams below show two types of motherboard, AT and ATX, with two different style of processor socket, Socket 7 and Slot 1. The ATX design came in at approximately the same time as the Pentium II, which used a slot 1 connector.

The quickest method of telling which one has been fitted to a machine is that generally an AT motherboard will have its peripheral sockets arranged in a line across the back of the board, whereas an ATX motherboard will generally have its peripheral sockets in a block in one corner at the rear of the motherboard.

The diagram below shows an AT motherboard with a Socket7 type ZIF socket for the processor. The Keyboard and mouse connectors will be PS/2 types.

The Serial, USB and Printer connectors will generally be mounted on metal plates that fix to the slots in the rear of the case for extension cards. The middle PCI and ISA slots usually share the same backplane and therefore only one card can be fitted, either ISA or PCI.
The Lithium battery is for a Real Time Clock (RTC), normally included on a Complimentary Metal Oxide Semiconductor (CMOS) IC with some RAM, which holds the configuration settings of the machine. A CMOS IC has been used as the current consumption is very low, this means that the battery will last about 5 years under normal use.
IDE controller sockets have been fitted to enable the hard disks to be connected via ribbon cables. The floppy disc drive(s) is (are) also connected via a ribbon cable to an IDC socket on the motherboard. In the case of the floppy disc the controller is fitted to the motherboard. The mouse and keyboard connectors may be the PS/2 or the earlier AT type connector.

The Power Supply connection to the motherboard is usually two plugs that connect to a single socket. Always ensure that the ends of the plugs that contain the black leads are together in the middle of the socket.
The diagram below shows an ATX type motherboard. Although this shows a Socket 1 type processor socket, versions are available with ZIF type processor sockets.

This type of motherboard is easily identified by the connection to the power supply on an ATX board this is a single plug and socket with a double row of pins. Generally this type of motherboard will only have DIMM sockets as SIMM memory modules were outdated before the type of processor that utilises the ATX board came in. The diagram shows integrated sound and SCSI but not all ATX boards have this.
The Serial, Parallel, USB, keyboard and mouse sockets are soldered directly to the motherboard in a cluster.
There may be an LED on the motherboard, which will light when it is in the standby mode.
This type of board may also have settings in the CMOS configuration that show the speed of various fans attached and the temperature of the processor(s). The ATX power supply to the motherboard has the same 3.3v output and power management as the notebooks and can be switched on or off by a signal from the motherboard. The positioning of the fan from the power supply also blows air directly across the processor, which very often reduces the need for a fan on the CPU, and just has a requirement for a simple heatsink. An ATX board will not fit into an AT case due to its positioning of the peripheral ports.