The Motherboard is a square or rectangle-shaped printed circuit board that serves as the central connectivity between components in most electronic devices, including personal computers and laptops, as well as home consoles. Nearly every component plugs into the Motherboard in some way, such as graphics cards, sound cards, floppy disk drives, hard disk drives, processors, solid state drives, RAM, fans, modems, power supply units, and anything else that connects via external ports, such as printers, scanners, microphones, mice, keyboards, joysticks, monitors, speakers, headsets, and many more.
Over the years, connections and their underlying transport technologies have evolved to ensure that data gets delivered as fast as possible across the system.
Expansion cards (the collective name for all plug-in daughterboards that use one of the long-slot buses) originally began with the 8-bit IBM PC-XT bus in 1981, which allowed users to replace MGA (Monochrome Graphics Array) displays with CGA (Color Graphics Array) displays via specialized graphics cards. From 1984 onwards, this bus began to be replaced with the 8-bit IBM PC-AT ISA (Industry Standard Architecture) bus, which could be used with more hardware; the original Creative SoundBlaster, which used ISA, became ubiquitous, and software became quite adept over time at directly manipulating this hardware, which in part led to the lifespan of ISA being longer than it would have been otherwise. IBM made an attempt to replace the ISA bus with the 32-bit MCA (Micro Channel Architecture) bus in 1987, but faced competition from the non-IBM 32-bit EISA (Extended Industry Standard Architecture) bus, which arrived in 1988, having been developed by a consortium of competitors. While MCA would find its niche through IBM's channel, EISA didn't make much of an impact on the IBM PC clone market, and ISA remained the de facto hardware standard for expansion cards. In 1993, the 32-bit VESA Local Bus was introduced, but it never made the desired impact due to the introduction of the robust 32-bit PCI Peripheral Component Interconnect bus; the PCI standard would also be available in a 64-bit extension known as PCI-X (Peripheral Component Interconnect eXtended), normally intended for servers and workstations, offering full backward-comaptibility with normal 32-bit PCI expansion cards in addition to the new 64-bit PCI-X expansion cards. PCI became the new de facto standard for most expansion cards, although the demand in bandwidth for graphics cards would later spur Intel to develop a graphics card-only successor standard, AGP (Accelerated Graphics Port), which functioned as a superset of the PCI standard. AGP was officially extended via AGP Pro, which used a longer slot and additional power for business-specific cards, usually for computer-aided design. AGP cards originally ran in either 1X or 2X modes (as defined by version 1.0 of the AGP specification), but later cards shipped with a 4X mode (as defined by version 2.0 of the AGP specification), with cards running in 8X mode (as defined by version 3.0 of the AGP specification) possible by the end of AGP's lifespan.
PCI also saw off a challenge from so-called "Riser" cards. Riser cards would operate like a normal expansion card, but would accept additional daughterboards at a right-angle. This was intended as a space-saving feature, which allowed Motherboard maufacturers to make smaller Motherboards that didn't have to incorporate features that could be instead be provided by plugging the appropriate card into the Riser card. Three main Riser standards evolved: AMR (Audio/Modem Riser), CNR (Communication And Networking Riser), and ACR (Advanced Communications Riser). Only one of these Riser slots would ever be present on a Motherboard, and all of the standards were designed for audio and communications hardware. AMR and its successor, CNR, were both developed by Intel, and the unique selling point was for motherboard manufacturers to avoid lengthly delays with clearing analog I/O components with the FCC (Federal Communications Commission, allowing a much shorter ceritifcation process with the motherboard manufacturer only needing to obtain a (much-quicker) ceritifcation for the daughterboard for the parent AMR or CNR expansion card their card would slot into. A consortium of competitors would later develop ACR, and this standard would have two clear advantages over CNR; first ACR would accept older AMR daughterboards, which CNR expansion cards could not accept, and in addition to supporting analog I/O hardware, ACR also had support for digital I/O hardware such as DSL modems. For mobile devices, Intel would develop the MDC (Mobile Daughter Card) specification (which was just a mobile version of AMR), which allowed for the addition of specific daughterboards for Ethernet (Ethernet Daughater Card), Modem (Modem Daughater Card), and Bluetooth (Bluetooth Daughater Card).
PCI, PCI-X and AGP would all later on be superceded by PCI Express (Peripheral Component Interconnect Express). PCI Express bus slots get progressively bigger the more lanes they support, with slots capable of, depending on size, supporting 1, 2, 4, 8 or 16 lanes. In practice, most expansion cards use 1 or 4 lanes, with graphics cards using between 8 and 16 lanes (depending on the specific Motherboard and configuration).
While there have been many methods devised to transfer data to storage devices (such as floppy disk drives and hard disk drives), only a few became mainstream. In 1986, ANSI (American National Standards Institute) ratified SCSI (Small Computer System Interface). This was later largely (but not completely) superceded by IDE (Integrated Drive Electronics) in the early 1990s under its official name, ATA (Advanced Technology Attachment). In 2003, version 1.0a of the Serial ATA Specification was released, with version 2.0 and 3.0 increasing the maximum bandwidth for devices confirming to those specification versions. The latest specification is verson 3.5 as of July 2020, and is as of December 2020 the most widely-used internal interface for data transfer between storage devices. SCSI would be superceded with SAS Serial Attached SCSI beginning in 2004. As SAS is designed for Enterprise customers, the maximum data bandwidth is much bigger compared to Serial ATA. While Serial ATA 3.0 (ratified in 2008) is capable of 6.0 Gbits/s, SAS-4 (ratified in 2017) is capable of 22.5 Gbits/s.
The PCI Express Mini Card (Mini PCIe) was introduced to replace the older Mini PCI standard, with some notebooks using a variant of the bus called mSATA for small solid state drives. While both of these standards were used in mobile devices (such as laptops), the usefulness of their compact form led to the creation of the PCI Express M.2 standard, with solid state drives falling under the NVM Express standard, which is compatible with both SATA Express and the PCI-e M.2 standard. M.2 connectors have started to be incorporated both dekstop PCs and video game consoles (both the PlayStation 5, Xbox Series X and Xbos Series S use a soldered-on M.2 solid state drive).