PCI, PCI-E and AGP Simplified

28 Feb

So you want a new graphics card, or rather you need a new graphics card since your old one is now obsolete and not supported by Windows 7? It’s probably best to have a cup of tea ready before going through this lot.

You’ve probably heard the terms PCI (Peripheral Component Interconnect), AGP and PCIe (PCI-E or PCI-Express) flying around, but which is right for you, and also, which will fit your machine? First came PCI, then AGP and now PCIe is all the rage.

Firstly, this is what the various slots actually look like:

PCI (you’re probably most familiar with this):

AGP:

PCIe:

Nowadays you will struggle to get hold of decent spec PCI and AGP graphics cards. Really, if the only option available to you is PCI or AGP, it’s probably time to upgrade your motherboard to one that supports PCIe.

Why? Well, this is a list of the various buses and their maximum bandwidth: (from here)

  • PCI – 132 MB/s
  • AGP – 8X2,100 MB/s
  • PCI Express 1x – 250 [500]* MB/s
  • PCI Express 2x – 500 [1000]* MB/s
  • PCI Express 4x – 1000 [2000]* MB/s
  • PCI Express 8x – 2000 [4000]* MB/s
  • PCI Express 16x – 4000 [8000]* MB/s
  • PCI Express 32x – 8000 [16000]* MB/s
  • USB 2.0 (Max Possible) – 60 MB/s
  • IDE (ATA100) – 100 MB/s
  • IDE (ATA133) – 133 MB/s
  • SATA – 150 MB/s
  • SATA II – 300 MB/s
  • Gigabit Ethernet – 125 MB/s
  • IEEE1394B [Firewire 800] – ~100 MB/s

*Since PCI Express is a serial based technology, data can be sent over the bus in two directions at once. Normal PCI is Parallel, and as such all data goes in one direction around the loop. Each 1x lane in PCI Express can transmit in both directions at once. In the table the first number is the bandwidth in one direction and the second number is the combined bandwidth in both directions. Also please note that in PCI Express bandwidth is not shared the same way as in PCI, so there is less congestion on the bus.

So, now you have a motherbaord that probably has 2 PCIe slots, just to confuse matters. Which do you use? Well for graphics anyways, you will want to use the PCIe x16 port, you will find that nearly all of the graphs cards available are x16. The x1 port(s) will most probably best be used utilised for network cards, and anything that is currently running on a PCI port.