Expansion Slots

They are present on every motherboard and are small plastic slots, usually few inches long and usually 1⁄2 inch wide. These slots are used to install various devices in PC to increase its capabilities. Circuit board inserted to add new capabilities to PC are called expansion boards, expansion cards , cards , add-ins , and add-ons. Usually video, network, sound, and disk interface cards are installed in these slots. Common types of expansion slots used are

  • ISA
  • PCI
  • AGP
  • PCIe
  • AMR
  • CNR

They differ in the function they do and in their appearance and are illustrated as

ISA Slots

They were prevalent in older PC usually before 1997 and were 8 or 16-bit wide with no hot-plugging even though 32-bit were introduced . Industry Standard Architecture (ISA) expansion slots are usually black and have two parts: one shorter and one longer. Later PC had few ISA slots for backward compatibility but ISA was phased by PCI

PCI Slots

Peripheral Component Interconnect (PCI) is widely present on motherboards. They are short (3 inches long) and white. They are 32 or 64-bit wide and have 133 MBps or 533MBps capacity.

AGP Slots

Accelerated Graphics Port (AGP) slots are used mainly for video card use, for a high-speed, accelerated 3D graphics video as AGP gives a direct connection between the video circuitry and the PC’s memory by being 32-bit wide and have above 2000MBps capacity. They are brown and are located usually next to the PCI slots on the motherboard but shorter than the PCI slots. They were phased out in favor of PCIe.

PCIe Slots

PCI Express (PCIe) replaced AGP and PCI as it is faster than AGP while being flexible like PCI.  They are by being 32-bit wide and have up to 16GBps capacity with option of hot-plugging in specific types.

They are present on motherboards usually with PCI slots for backward compatibility. They are available in seven different speed levels and designated 1X, 2X, 4X, 8X, 12X, 16X, and 32X also their size expands as per the speed level thus 1X is extremely short (less than an inch) and for remaining; the longer the slot, the higher the speed.

A shorter (or lower-speed) card can be put in a longer (or higher-speed) slot the converse, is not true.

AMR Slots

Audio / Modem Riser( AMR) is a expansion slot for a riser  card found on the motherboards of some Pentium III and Pentium 4 PC. It was designed by Intel to interface with chipsets and provide analog functionality, such as sound cards and modems, on an expansion card. They are 46-pin slots  which is being phased by CNR and Advanced Communications Riser (ACR)

CNR Slots

Communications and Networking Riser (CNR) is a slot found on certain PC motherboards and used for specialized networking, audio, and telephony equipment. A motherboard manufacturer can choose to provide audio, networking, or modem functionality in any combination on a CNR card. CNR slots were once commonly found on Pentium 4-class motherboards, but have since been phased out in favor of on-board or embedded components. They are  60-pin slots. Advantages of CNR over AMR include networking support, Plug and Play compatibility  and no need to lose a competing PCI slot unless the CNR slot is in use.

Bandwidth Table
PCI133 MB/s
AGP 8X2,100 MB/s
PCI Express 1x400 MB/s
PCI Express 4x1600 MB/s
PCI Express 8x3200 MB/s
PCI Express 16x6400 MB/s

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