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Speed testing -x16 vs. -x1 with PCI Express video cards
1. IntroductionOur xprs-px-x16 product allows using of PCI Express -x16 cards, outside of computer systems through cables. For details on the way of use, you can check this article .
Number of our customers, interested in using this product, asked technical details. The xprs-px-x16 allows using of a PCI Express -x16 card, through -x1 link and cables.
In general, one -x16 card, has 16 transmit and 16 receive pairs/lines. One -x1 card, has 1 transmit and 1 receive pair/line. Theoretically a -x16 card has to be 16 times faster than one -x1 card.
PCI Express interface allows the work of a card, using the smaller number of transmit/receive pairs.
This article compares the speed difference when the same -x16 card works using all 16 transmit/receive pairs, and when the card works using 1 transmit/receive pair.
2. Way of testingPCI Express -x16 card normally is mounted on a desktop motherboard.
(click on image to enlarge)
The above image is a very simplified representation of mounting. A desktop motherboard is normally mounted in a box, hooked to a power supply ... etc.
The image below shows the same video card mounted on our xprs-px-x16 product, connected through 1m cables, to xprs-host-dt mounted on the same motherboard.
The above image is a also simplified representation of mounting. The xprs-px-x16 product has to be connected to a power supply in order to power on the PCI Express -x16 card.
3. Cards and testsThe tests wre performed on 2 video cards, both of them based on NVIDIA chips:
- geforce 8400 card, 512mb memory (card on right side)
- geforce GT 430 card, 1gb memory (card on left side)
As a result of a web search for doing a benchmark test on a video card, we picked 2 tests:
- by Freestone-Group - free download
by Passmark Software - 30 days free for evaluation, cost
The Freestone-Group test software (image above) is only for benchmarking video cards and gives a single score as the end result.
The Passmark test software (image below) is for general benchmarking of a system, includes 2D and 3D tests for video cards, and gives separate scores for the each of the sub-tests.
4. Test resultsThe Freestone-Group test gives these scores:
Card -x16 -x1 Difference '8400' 44 40 9% 'gt 430' 238 231 2.9%
The Freestone-Group mix of tests like the above show a very small difference between -x16 and -x1 mode.
The Passmark test gives these scores for '8400' card:
Test -x16 -x1 Difference Graphics 2D - Solid Vectors: 0.9 0.9 0 Graphics 2D - Transparent Vectors: 0.9 0.8 11.1% Graphics 2D - Complex Vectors: 87.1 84.1 3.4% Graphics 2D - Fonts and Text: 36.3 28.8 20.6$ Graphics 2D - Windows Interface: 14.0 11.2 20.0% Graphics 2D - Image Filters: 92.3 88.4 4.2% Graphics 2D - Image Rendering: 202.2 141.5 30.0% Graphics 3D - Simple: 130.5 83.1 36.3% Graphics 3D - Medium: 50.6 34.4 32.0% Graphics 3D - Complex: 14.7 2.3 84.3% !!! Graphics 3D - DirectX 10: 0.9 0.9 0 2D Graphics Mark: 157.7 135.7 13.9% 3D Graphics Mark: 117.9 65.7 42.2%
The Passmark test gives these scores for 'gt 430' card:
Test -x16 -x1 Difference Graphics 2D - Solid Vectors: 1.0 1.0 0 Graphics 2D - Transparent Vectors: 1.0 1.0 0 Graphics 2D - Complex Vectors: 91.4 77.4 15.3% Graphics 2D - Fonts and Text: 36.1 35.5 1.6% Graphics 2D - Windows Interface: 14.0 14.0 0 Graphics 2D - Image Filters: 92.6 92.4 0.1% Graphics 2D - Image Rendering: 203.7 203.1 0.3% Graphics 3D - Simple: 406.5 396.9 2.3% Graphics 3D - Medium: 271.3 204.5 24.6% Graphics 3D - Complex: 16.0 4.0 75.0% !!! Graphics 3D - DirectX 10: 7.4 4.9 33.7% 2D Graphics Mark: 162.1 156.0 3.7% 3D Graphics Mark: 460.0 337.5 26.6%
The tests show a very small difference for the 2D Graphics tests.
A large difference appears for the Complex 3D Graphics test. However the larger the video memory is and the better/faster the GPU - the gap between -x16 and -x1 modes gets smaller.
Conclusion - a PCI Express -x16 card placed in '-x1' mode is getting most of the performance, and may be good enough solution in case of using a peripheral card outside of a computer system, through a cable.
5. DIY (do-it-yourself) testingWhile we did test with 2 video cards, they are most likely different your own video card(s).
If you are curious about what the difference is between -x16 and -x1 modes for your video cards, there is a way to find this.
The PCI Express connectors have compatible pin-outs - with the signals on the pins on the -x1 connector identical to the respective pins for the part of the -x16 connector.
In practice this means that you can plug one -x1 card into a -x16 connector an it will still work.
The opposite is also true - using a tape, you can cover the additional pins of one -x16 card, and leave exposed only pins matching -x1 connector.
When you plug a -x16 video card prepared in such way in a motherboard, it will be forced to operate in -x1 mode.
Then you can run some of the above tests or any other test you like.
After testing, when the tape is removed, please make sure the pins on the -x16 card are cleaned with alcohol or other solutions.
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