# Sticky  AGP, PCI and PCI-Express - A Primer



## ebackhus

One of the questions we often get is "what kind of card can I put in my PC?" To answer that we often ask what type of slots are available. Being experienced computer technicians we can tell at a glance what type of slots are in a PC but the average user is often confused by the myriad of connectors in their computer. I'm putting together this primer to help you help us with knowing your PC just a little more.

I'll be discussing the three common connector types in computers. They are called AGP, PCI and PCI-Express.

AGP was a connector type developed to better send data to the more powerful video cards that were entering the market. Prior to AGP video cards used the PCI bus which could hurt performance in that the PCI bus is rather slow (comparatively) and other devices on the PCI bus would further consume available bandwidth and speed. AGP overcame this by giving the video card a dedicated path from communications to the CPU and RAM. AGP comes in three revisions and also the AGP Pro type connector. The three revisions are also used to determine that actual throughput of the connector itself.







This is a typical AGP slot. Note that it is closest to the CPU socket, unlike PCI and PCI-Express which can be in any location on the back plane of the motherboard.


PCI, the oldest in this primer, has been around since the mid 90's and is a very universal and adaptable connector type. With early video cards and 3D accelerators the PCI bus provided a much-needed increase in speed from the older ISA bus. PCI doubled the bandwidth going from 16-bit to 32-bit and also gave the advantage of bus mastering, allowing performance far beyond what ISA could ever offer. As cards evolved, however, tge PCI bus became to slow and easily congested for more powerful video cards.







The white slots in this photo are PCI slots. While quite useful for a number of various expansion cards, video cards have long outgrown this connector type.

PCI-Express went back to the previously unpreferred Serial bus to increase speed and bandwidth. Advances in technology and manufacturing had once again made Serial connections a viable technology and the advantages it would offer for video cards made it worth creating a new connection type for. PCI-Express has three basic connector types, each with successively more speed and bandwidth. The first is 1x. This is useful for most modems, network cards, sound cards, and some basic video cards. 8x increases the speed further and can be used for the same devices as 1x but with increased performance. This is often the minimum preferred for video cards unless 3D gaming isn't desired. 16x offers even further speed and is the most widely preferred connection for high performance video cards and disk controller cards. PCI-Express version 2.0 increases speeds to 32x which is well beyond what most computers can actually use. An important thing to note is that most video cards that are designed for 2.0 will NOT work in 1.0 slots. They will, however, work in 1.1 slots. PCI-Express also allows for the use of multiple video cards. nVidia calls their multi-card configuration SLI. AMD/ATi calls their multi-card configuration CrossFire and more recently, CrossFireX. The benefits of using multiple cards are a hot topic in most computer communities.







The blue and black slots on this motherboard are PCI-Express 16x slots. The small white slots are PCI-Express 1x slots. Note that they are reverse of PCI and slightly offset. This prevents improper installation of devices.







This image shows all three connector types on a single board. The dark orange slot is PCI-Express, the light orange slot is AGP and the white slots are PCI.


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## ebackhus

This chart on www.hardwaresecrets.com does an excellent job of explaining what type of PCI-Express slot your motherboard comes with.


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