The functions of a computer motherboard are as follows. The motherboard also acts as the platform on which various expansion slots are available to install other. An expansion card is an electronic circuit board that adds more functionality to a desktop computer.These cards are installed into the expansion slot of a computer motherboard, and they allow the computer to perform additional functions not offered by the motherboard. Our Expansion Slot Conversion and Extension products offer simple solutions for adapting or converting expansion cards for compatibility with the host system or laptop.

An expansion card is an electronic circuit board that adds more functionality to a desktop computer. These cards are installed into the expansion slot of a computer motherboard, and they allow the computer to perform additional functions not offered by the motherboard. Video cards and sound cards are common examples: a new video card added will enhance the three dimensional graphics processing power of a computer while a new sound card may improve a computer’s audio input.

There are alternative terms used for this type of card, and it is also known as expansion board, add-on card, interface adapter or an internal card. Generally, between one and seven expansion cards can be installed into the desktop computer system. Laptops do not use standard cards due to their small form factor, although they can often accept a removable PCMCIA card that offers additional functions.

The Altair 8800, developed in the mid 1970s, was the first microcomputer to add an expansion card bus. In 1981, IBM® launched its first PC with an XT bus, which was later replaced with a 16-bit ISA. The introduction of the PCI bus in 1991 resulted in modern forms of interface adapters that provided additional benefits beyond enhanced graphics and sound.

Most cards are inserted in PCI or “Peripheral Component Interconnect” slots, which are integrated circuits fitted onto the motherboard. One edge of the card holding the contacts or keys is inserted into the slot. This establishes an electrical contact between the motherboard and the card’s integrated circuits.

Standard interface adapters, such as graphics cards and sound cards, offer various added functions. Some video cards offer video capture, MPEG 2 and MPEG 4 decoding, a light pen, and the ability to connect to multiple monitors, for example. Sound cards may add functions for composing music, editing audio presentations, and other multimedia applications.

There are some “low-profile” cards that fit in a lower height computer framework. Some are used solely for external connectivity such as modem cards, storage area network (SAN), and network cards, which are commonly referred to as I/O cards or input/output cards. A USB card is mainly used by users who need additional USB or Firewire ports.

A PC expansion card can only be inserted on computers with available expansion slots. Computers such as the Apple Macintosh® and other all-in-one systems do not accept these cards.

The most visible parts of any motherboard are the expansion slots. An expansion slot of a computer motherboard is used to accept the expansion card or expansion board, adapter card or accessory card to add additional functionality to a computer system. There are many types of expansion slots used in today's computers. They are ISA, PCI, AGP, PCIe, AMR, and CNR expansion slot. Each type differs in appearance and function.

ISA Expansion Slots

The computer made before 1997, the motherboard has a few ISA, Industry Standard Architecture, expansion slots. They're easily recognizable because they are usually black and have two parts: one shorter and one longer. Computers made after 1997 generally include a few ISA slots for backward compatibility with old expansion cards.

PCI Expansion Slots

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Most computers made today contain primarily PCI, Peripheral Component Interconnect, slots. They are easily recognizable because they are short (around 3 inches long) and usually white. PCI slots can usually be found in any computer that has a Pentium-class processor orhigher.

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AGP Expansion Slots

AGP, Accelerated Graphics Port, slots are very popular for video card use. In the past, if you wanted to use a high-speed, accelerated 3D graphics video card, you had to install the card into an existing PCI or ISA slot. AGP slots were designed to be a direct connectionbetween the video circuitry and the PC's memory. It uses the northbridge bus so it is very fast. They are also easily recognizable because they are usually brown, are located right next to the PCI slots on the motherboard, and are shorter than the PCI slots.

PCIe Expansion Slots

PCIe X1

PCIe X4

PCIe X8 and 16

The newest expansion slot architecture that is being used by motherboards is PCI Express (PCIe). It was designed to be a replacement for AGP and PCI. It has the capability of being faster than AGP while maintaining the flexibility of PCI. It also uses the northbridge bus. And motherboards with PCIe will have regular PCI slots for backward compatibility with PCI.

There are seven different speed levels for PCIe, and they are designated 1X, 2X, 4X, 8X, 12X, 16X, and 32X. These designations roughly correspond to similarly designated AGP speeds. The slots for PCIe are a bit harder to identify than other expansion slot types becausethe slot size corresponds to its speed. For example, the 1X slot is extremely short (less than an inch). The slots get longer in proportion to the speed; the longer the slot, the higher the speed. The reason for this stems from the PCIe concept of lanes, which are the multiplied units of communication between any two PCIe components and are directly related to physical wiring on the bus. Because all PCIe communications are made up of unidirectional coupling between devices, each PCIe card negotiates for the best mutually supported number of lanes with each communications partner.

AMR Expansion Slots

As is always the case, Intel and other manufacturers are constantly looking for ways to improve the production process. One lengthy process that would often slow down the production of motherboards with integrated analog I/O functions was FCC certification. The manufacturers developed a way of separating the analog circuitry, for example, modem and analog audio, onto its own card. This allowed the analog circuitry to be separately certified (it was its own expansion card), thus reducing time for FCC certification. This slot and riser card technology was known as the Audio Modem Riser, or AMR. AMR¡¯s 46-pin slots were once fairly common on many Intel motherboards, but technologies including CNR and Advanced Communications Riser (ACR) are edging out AMR. In addition and despite FCC concerns, integrated components still appear to be enjoying the most success comparatively.

CNR Expansion Slots

CNR, Communications and Networking Riser, slots that can be found on some Intel motherboards are a replacement for Intel's AMR slots. Essentially, these 60-pin slots allow a motherboard manufacturer to implement a motherboard chipset with certain integrated features. Then, if the built-in features of that chipset need to be enhanced (by adding Dolby Digital Surround to a standard sound chipset, for example), a CNR riser card could be added to enhance the onboard capabilities. Additional advantages of CNR over AMR include networking support, Plug and Play compatibility, support for hardware acceleration (as opposed to CPU control only), and no need to lose a competing PCI slot unless the CNR slot is in use.

SATA Expansion Slots

SATA is a new standard for connecting hard drives into computer systems. As its name implies, SATA is based on serial signaling technology, unlike current IDE (Integrated Drive Electronics) hard drives that use parallel signaling.

SATA has several practical advantages over the parallel signaling (also called Parallel ATA or PATA) that has been used in hard drives since the 1980s. SATA cables are more flexible, thinner, and less massive than the ribbon cables required for conventional PATA hard drives. SATA cables can be considerably longer than PATA ribbon cables, allowing the designer more latitude in the physical layout of a system. Because there are fewer conductors (only 7 in SATA as compared with 40 in PATA), crosstalk and electromagnetic interference (EMI) are less likely to be troublesome. The signal voltage is much lower as well (250 mV for SATA as compared with 5 V for PATA).

SCSI Expansion Slots

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SCSI, Small Computer Serial Interface, is a series of interface standards for disk drives and other peripherals, usually offering better performance than the IDE interface standard in PCs but with more complexity and at higher cost.