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PCI Express (PCIe) cards became available in 2003 and slowly replaced the older AGB and PCI video cards.  If your system has PCIe slots available (see below to identify card slots), a PCIe card is the best choice for an upgrade. PCIe specifications include a stipulated or designed maximum data rate that the motherboard should support. 

PCIe Data Rates

The typical PCIe graphics card slot in the motherboard has 16 lanes for communicating data back and forth to the video card. The first generation standard, PCIe 1.0, specified a data rate of 250 MB/s per lane, which calculates to a total maximum data rate (or bandwidth) of 4 GB/s for the 16 lanes.  PCIe 2.0, a specification upgrade introduced in 2007, doubled the maximum data rate. PCIe 3.0, released in November 2011, doubled it again.  The first motherboard with PCIe 3.0 slots was released in July, 2011. The fastest cards currently available for an upgrade are PCIe 2.0, and none, even the fastest, saturate or fully use the bandwidth of PCIe 2.0.

Maximum Data Rate
Per Lane
x16 Card Slot
PCIe 1.0
250 MB/s
4 GB/s
PCIe 2.0
500 MB/s
8 GB/s
PCIe 3.0
1,000 MB/s
16 GB/s

For more information about PCIe 3.0, see the following article, written in 2010:

PCI Express 3.0 On Motherboards This Time Next Year

While graphics cards all fit into an x16 slot on the motherboard, the processing speed of cards varies greatly depending on its computational power, with a wide range in performance and prices for different x16 graphics card models.  Only the faster cards can effectively utilize more than half the maximum data rate capacity of PCIe 2.0.

PCIe Video Card Connectors

closeup of the PCIe connectors on the GTS 450 card

PCIe connector on the GTS 450 video card

PCIe specifications are designed for forward and backward upgrade compatibility between generations.  For example, you can put a 2.0 card into a 1.0 motherboard or vice versa.  The data transmission rate between the two will be limited by the slower of the two components.

Both nVidia Geforce and ATI Radeon HD video cards comply with the PCIe specifications so either type will work in most motherboard when you upgrade. However, some motherboards only support using one or the other in tandem with a second similar card. 

The picture at right shows the PCIe connectors on the bottom of the GTS 450 that go into the motherboard slot.

Because most video cards use less than half the capacity of the standard PCIe 2.0 slot, some motherboard manufacturers chose to split or share lanes.  One standard chipset design for motherboards provided by Intel even requires this. In such cases, the motherboard still has the physical x16 slot to accommodate video cards, but typically only provides an x8, or half speed, data rate.  For some designs, this is the native rate for its physical x16 slot.  In other cases the motherboard may have two or more x16 slots sharing lanes so that if only one card is used it runs at x16 capacity but if two slots then both slots run at x8 speed or capacity.  With the “average” video card, which has a peak data rate less than half the PCIe 2.0 maximum, the user will not notice any difference between physical x16 slots that operate at x8 or x16 speeds.

PCIe Motherboard Slots

picture of video card slots on motherboard

PCI Express Slots (from top to bottom: ×4,
×16, ×1 and ×16), compared to a traditional
32-bit PCI slot (bottom)

The PCIe connectors or slots on the motherboard are different than those used for PCI and AGP cards. The PCIe slots are designed for faster data communication rates and provide more power directly through the slot to the video card.  The three standards are not compatible with one another – you cannot put a PCIe card into an AGP or PCI slot - you cannot upgrade from one type to another if the motherboard does not have the right slots. 

Since PCIe cards are used for many functions besides graphics cards, such as audio cards and add-in USB, Firewire, and eSATA cards, they come in several lengths that vary in the number of channels, called “lanes”, which they have and consequently in data rate capacity.  Standard configurations include 1, 2, 4, 8, 16, and 32 lanes.  As noted above, video cards typically have 16 lanes, and fit into a card slot on the motherboard designed for x16 cards (see photo at right). 

Note the close spacing of the slots. Some graphic cards are wider than others and when installed will cover the adjacent slot. Before and upgrade to such a wider card, you need to verify that the adjacent slot on the motherboard is open, or can be made open by moving or removing the adjacent card.



If you plan to upgrade just the video card and not the motherboard, it is a good idea to verify that your motherboard has a PCIe x16 slot and to identify which generation it is.  You should be able to learn both from your system or motherboard manual.  If you don’t have the manual, you may be able to get an online manual from the system or motherboard manufacturer.  For the latter, if you don’t know the motherboard model number, you should be able to get it off the board inside the computer. If no manual is available, you can still verify the presence of an x16 slot by looking at the motherboard and comparing the slots with the ones shown above.

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