The motherboard (English mainboard, also motherboard ) is the main circuit board of a computer. On it, the individual components such as the main processor are (CPU), memory, the BIOS chip with embedded firmware, the interface modules and slots for expansion cards mounted; the necessary circuit paths are divided into several layers ( Layer).


The motherboard contains slots for the processor, memory modules, and expansion cards such as graphics, sound and network cards and modules that connect the components together. The former division into a Northbridge for high- performance connection of memory and graphics card and a Southbridge for hard drive, PCI slots and peripherals currently disappears (2010). Functions such as memory controllers are now integrated into the CPU itself, so a two-chip design was unnecessary. Some still continue to speak of a Southbridge chipset, although it is actually only a key component on the motherboard.

Many former individual components are already permanently integrated on the mainboard ( "onboard "), especially sound and network cards are virtually without exception standard and satisfy the needs of many users. Unlike notebooks are onboard graphics cards to find rare in the desktop area although it may well provide sufficient performance for office computer. Faster, games enabled graphics cards continue to have just as a plug-in card - the part of the processor manufacturers, there is however the effort, CPU and GPU reunite. Also found at the interfaces in the course of time an integration is performed on the main board. While in the past even standard connections such as serial ( "RS- 232" ) and parallel ( " LPT " ) interface have been implemented only on cards, today all the usual ports are already present on the motherboard. Multiple USB ports are an integral part of each I / O Shields, as well PS/2-ports for mouse and keyboard (some only as a combo port), the aforementioned audio and network connections, and, depending on the orientation of the board, video -, eSATA, FireWire and other ports. Sometimes, rarely used connections must be swapped for reasons of space to slot panels, so as even a game port can be provided. The former variety of different connections for external components is now completely gone and replaced by USB.

For various internal components Serial ATA ports ( "SATA " ) are on the motherboard also provided, which has become a standard for hard drives and optical drives. ATA / ATAPI ( " PATA " ) interfaces are, if at all, only once available, whereas previously two ( primary and secondary ) were common to connect up to four drives. Connectors for floppy drives are also only likely to be half of the current motherboards still existed. Again accepts an interface type to connect all components, with the substitution of the disk through USB sticks plays a role.

In the slots ( engl. slots) for expansion cards the development of XT- bus via the ISA bus, EISA bus, the PCI bus ran to the PCI Express bus (PCIe ), the present (2010) in the non-professional ( "consumer " ) area is current. In the Server field PCI -X is up to date, here again the transition to PCIe is completed. Furthermore, there were parallel developments such as the MCA bus and special slots for graphics cards such as the VLB and the AGP slot. These are now replaced fully by PCIe.

Slots are now almost exclusively occupied when in a task pane particularly high performance is required, which can not be supplied by the onboard components. All of these cards have their own processors, which relieve the main processor of the system and are optimized for the specific application. Onboard components can, however, perform calculations from the CPU, so their performance can break under high load of the computer. Apart from graphics cards in particular hard disk controller are common components that can provide RAID functionality for up to 28 SAS or SATA hard drives in professional systems. They are also at defect without loss of data exchanged, which is not possible with onboard RAID, and having separate units for the XOR parity computation. There are also single-or multi-port NICs for copper and fiber optic networks as well as sound cards with extensive digital and analog inputs and outputs. For controller cards antiquated ports such as RS- 232 PCI interface is quite sufficient, while current USB 3.0 expansion cards are on the high data rate of PCI Express x1 or higher dependent.


The format of the motherboards is distinguished by the form factor. Since 1995, the ATX form factor is current. It replaced the AT- format and brought several changes to cases and power supplies with it. There are several variations of ATX and AT in order to equip more compact devices without proprietary formats, such as Baby AT or uATX. Mini - ITX, Flex -ATX and Micro -ATX fit into ATX case. Slots, screws and the window for I / O Shield located on uniform or the same position.

The ATX form factor was to be replaced from 2003 by the so incompatible BTX, BTX but could not prevail and verschand 2007 from the market. BTX in the plug-in cards on the other side of the main circuit board are arranged to ATX. Wherein the main board is located on the other side wall of the housing. With vertically integrated motherboards This proved to the location of the cooling body of plug-in cards.

AMD had announced the beginning of September 2007 DTX format that is intended for frugal users because it is smaller and also for the most part ATX - compatible.

Example of an ATX motherboard (2010)

More images of typical motherboards

AT motherboard for 80286 CPUs and 16 -bit ISA slots, in the late 1980s

80286 Baby AT motherboard 1988

Motherboard with 80386DX CPU in AT format in the early 1990s

Mainboard from Dell System 325P with i386DX LPX format slots only LPX riser card, built in 1990

AT motherboard for 80486 CPUs.

Socket 7 AT motherboard, with longitudinal controller for CPU voltages, built in 1996

Super Socket 7 ATX motherboard with down converter for CPU core voltage, built in 1998 and 1999

Only four layer ATX motherboard with Socket 462 for AMD CPUs and SiS735 chipset in a chip, built in 2001

Server motherboard for two AMD Opteron CPUs

BTX with AM2 Socket

ATX motherboard for Socket 775 (supports Core 2 Duo / Quad ), 2008, supports SLI. CPU and RAM are already installed.

ATX - Socket 1155 covered - the North Bridge, and usually also a GPU are integrated into this architecture to the CPU, PCI and PCIe 1x and 16x, DDR3 RAM, 2011

Mini - ITX board, CPU and chipset passively cooled 2008

Nano-ITX Board with approved heat sinks, S0 RAM sockets, CPU soldered 2008

Pico -ITX board with approved heat sinks, CPU soldered 2008

Logic Board an iPhone, typical design of the motherboard in a smartphone