Expansion Slot

Expansion port or Bus slot  an Expansion slot is a slot located inside a computer on the motherboard or riser board that allows additional boards to be connected to it. For example, if you wanted to install a new video card in the computer you'd purchase a video expansion card and install that card into the compatible expansion slot. Below is a listing of some of the expansion slots commonly found in computers and the devices commonly associated with those slots. 

Computer expansion slots

• AGP - Video card
• AMR - Modem, Sound card
• CNR - Modem, Network card, Sound card
• EISA - SCSI, Network card, Video card
• ISA - Network card, Sound card, Video card
• PCI - Network card, SCSI, Sound card, Video card
• PCIe - Video card
• VESA - Video card

AMR

Released September 8, 1998, AMR is short for Audio/Modem Riser and allows OEMs to make one card that has the functionality of either Modem or Audio or both Audio and Modem on one card. This specification allows for the motherboard to be manufactured at a lower cost and free up industry standard expansion slots in the system for other additional plug-in peripherals.


CNR
Short for Communication and Network Riser, CNR is a specification that supports Audio, Modem, USB, and LAN interfaces of core logic chipsets. This technology and the CNR slot was first introduced by Intel February 7, 2000 and was mainly developed by leading hardware and software developers who helped release the AMR (Audio Modem Riser) slot.


EISA
Short for Extended Industry Standard Architecture, EISA, also known as Extended ISA, is a standard first announced in September of 1988 for IBM and IBM compatible computers to compete with the IBM MCA bus. The EISA bus is found on Intel 80386, 80486 and early Pentium computers and was designed by nine competitors to compete with IBM's MCA bus. These competitors were AST Research, Compaq, Epson, Hewlett Packard, NEC, Olivetti, Tandy, WYSE, and Zenith Data Systems.

The EISA bus provided 32-bit slots at an 8.33 MHz cycle rate for use with 386DX or higher processors. In addition, the EISA can accommodate a 16-bit ISA card in the first row.
Although the EISA bus is backwards compatible and not a proprietary bus, it never became widely used and is no longer found in computers today.


ISA
Short for Industry Standard Architecture, ISA was introduced by IBM and headed by Mark Dean. ISA was originally an 8-bit computer bus that was later expanded to a 16-bit bus in 1984. When this bus was originally released it was a proprietary bus, which allowed only IBM to create peripherals and the actual interface. However, in the early 1980's other manufacturers were creating the bus.

In 1993, Intel and Microsoft introduced a PnP ISA bus that allowed the computer to automatically detect and setup computer ISA peripherals, such as a modem or sound card. Using the PnP technology, an end-user would have the capability of connecting a device and not having to configure the device using jumpers or dip switches.

All recent computers today no longer included the ISA slots and instead are using more PCI, AGP, and other slots. Below is a graphic of what an ISA expansion card may look like as well as the slot it connects into on the motherboard.


PCI
Peripheral Component Interconnect, PCI was introduced by Intel in 1992, revised in 1993 to version 2.0, and later revised in 1995 to PCI 2.1 and is as an expansion to the ISA bus. The PCI bus is a 32-bit (133MBps) computer bus that is also available as a 64-bit bus and was the most commonly found and used computer bus in computers during the late 1990's and early 2000's.

Originally known as 3rd Generation I/O (3GIO), PCI Express, or PCIe, was approved as a standard on July 2002 and is a computer bus found in computers. PCI Express is a serial bus designed to replace PCI and AGP and is available in several different formats: x1, x2, x4, x8, x12, x16 and x32. The data transmitted over PCI-Express is sent over wires called lanes in full duplex mode (both directions at the same time). Each lane is capable of around 250MBps and the specification can be scaled from 1 to 32 lanes. This means 16 lanes could support a bandwidth of up to 4,000MBps in both directions. Below are some graphic illustrations of what the PCI Express would look like on the motherboard.


VESA
Short for Video Electronics Standard Association, VESA is a group of monitor and video card manufacturers that set video display and bus standards. VESA was originally founded by NEC and is most well known for the VL Bus or VESA local Bus standard & first introduced in 1992. The VLB is a 32-bit computer bus that had direct access to the system memory at the speed of the processor.