PCIe x16 vs. x8, x4, x1

[Sasqui]

Very good read for those interested in finding out more about the differences between PCIe x16, x8, x4, x1 on video cards:

http://www.tomshardware.com/2007/03/27/pci_express_scaling_analysis/index.html

Interesting that they physically taped the lane connectors on the video card for the tests!

[LiNKiN]

Very interesting read indeed Sasqui! Interesting to see just how much bandwidth the 8800 needs!

[Pinchy]

Now we ask ourself - why are there motherboards that have their 2nd PCIe slot at only 4x :p

[Sasqui]

Very interesting read indeed Sasqui! Interesting to see just how much bandwidth the 8800 needs!

On the second page, they show the duplexing bandwidth - I suspect the 8800 doesn't take advantage of it like the 1900...

[Pinchy]

This is pretty much on topic, and i dont want to create a new thread about it.

With the ASUS p5b deluxe, it says the second PCIe slot (for XF) is 4x. But (refer to expansion slots: http://event.asus.com/2006/mb/P5B/models.html), the P5B deluxe and Wifi editions have

2 x PCI-E x16 (blue @ x16 mode, black @ x2 or x4 mode)


Sounds weird seeing as its 2x16x PCIe, yet the black is 4x or 2x(...anyways). If you look at the P5B-E plus and the P5B-VM, they have 1x PCIe 16x and 1x PCIe 4x....what the?

[Sasqui]

Sounds weird seeing as its 2x16x PCIe, yet the black is 4x or 2x(...anyways). If you look at the P5B-E plus and the P5B-VM, they have 1x PCIe 16x and 1x PCIe 4x....what the?

That's par for all 965 based boards (I think!). My DQ6 is 16x and 4x - both are 16x physical slots, but one only has 4x lanes.

[Pinchy]

Damn that sucks :(

[Completely Bonkers]

Interesting benchmarking... I'm surprised that Tom's was so late in doing the taping exercise. Many other sites have done it already.

The summary is that in most real-life situations (not benchmarking tools which are actually only benchmarking the bandwidth), that the performance ratios are: x16=100%, x8=98%, x4=85%. That means, an x8 lane is not noticeable slower than an x16, but an x4 is measurably slower... albeit, only 15% loss. However, Tom's analysis shows these ratios are for ATI GPUs and not nVidia which suffers much more.

And the interesting fact is that AGP DOES OPERATE as x8 speed. So AGP is not dead (yet).

It's a shame that the review didn't take X1950Pro or X1950XT card as well, and compare this to X1950Pro/XT AGP. Now THAT would have been truely interesting!

Personally, I will not be upgrading my mobo until PCIe v2.0, about 6 months away. In the meantime, I will upgrade my GPU... which therefore means I'm looking at an AGP X1950XT. http://geizhals.at/deutschland/a239982.html

[Pinchy]

The only problem with having an AGP system is that you can get a good processor or good RAM, or XF/SLi (Thats why I went to PCIe)

[WarEagleAU]

awesome stuff, Ill check it out now.

[Completely Bonkers]

The only problem with having an AGP system is that you can get a good processor or good RAM, or XF/SLi (Thats why I went to PCIe)Oh, but you can! You can get a Quad Core 2 Duo on AGP! See ASROCK site for many many mobo's. What's also nice, is that if you have 2 or 4 GB of fast DDR... you can use that on a Quad Core 2 Duo too. And it performs pretty well too... because of the better latency of DDR over DDR2 and the big cache of the Core 2 Duo.

While a whole new PC and memory may be (marginally) faster than the ASROCK setup... you save a BUNDLE not having to upgrade RAM or a good AGP GPU. See my specs as to why I'm not tossing my GPU just yet!

[Pinchy]

Oh, but you can! You can get a Quad Core 2 Duo on AGP! See ASROCK site for many many mobo's. What's also nice, is that if you have 2 or 4 GB of fast DDR... you can use that on a Quad Core 2 Duo too. And it performs pretty well too... because of the better latency of DDR over DDR2 and the big cache of the Core 2 Duo.

While a whole new PC and memory may be (marginally) faster than the ASROCK setup... you save a BUNDLE not having to upgrade RAM or a good AGP GPU. See my specs as to why I'm not tossing my GPU just yet!

Wow didnt know that.

Still though, wouldnt those mobos be expensive? And you are very limited in brands...(not dissing Asrock in any way - ive never used 1 so i dont know what its like)

But I dont know about overseas, but im sure that the AGP GPU's over here are heaps more expensive than the PCIe ones. Theres a $100 difference between the X1950 PRO's from AGP --> PCIe (Thats over half your PCIe mobo :p)

[kwchang007]

uh oh, so the whole asus xg station is not going to preform that well.....bummer....

[DanTheBanjoman]

Wow didnt know that.

Still though, wouldnt those mobos be expensive? And you are very limited in brands...(not dissing Asrock in any way - ive never used 1 so i dont know what its like)


Asrock is dirt cheap actually. They're not the best for overclockers or anything, though for normal use they're just fine.

[Pinchy]

Last time i checked, which was a while back, the asrock mobo i wanted (PCIe for socket 478) was uber expensive...


well, i think it was asrock :D


EDIT - Holy @#$%! They are really cheap :|

[tkpenalty]

Yeah.. $70 for a fully fledged motherboard that supports core 2 quad and 1066 mhz as well as ESATA.... PCI-E 16x and 8x.

[D-rock]

That's par for all 965 based boards (I think!). My DQ6 is 16x and 4x - both are 16x physical slots, but one only has 4x lanes.

Yes, thats correct. The P965 chip only supports 20 PCIe lanes. 16 lanes for the blue (on asus mobo) slot and 4 for the black slot. If you have a card in the X1 PCIe slot then the black slot, while its physically an x16 size it will revert to x2 lanes.

[Pinchy]

So that means the second card can only run at 2-4x?

Couldnt you split it, 8x and 8x? Or 10x and 10x :p

[Behemoko]

Nice find, I'm glad to see that we haven't yet needed 8x, even 6x would probably be enough for the 8800, so we seem pretty future proofed, (at least for a while anyway, lol)

[D-rock]

So that means the second card can only run at 2-4x?

Couldnt you split it, 8x and 8x? Or 10x and 10x :p

I guess that depends on your mobo. I have the P5B deluxe and it doesnt allow for that. But i know that some mobo's that use the 965 chip and do crossfire thats how they do it.

[Pinchy]

Maybe we will get a BIOS update that'll enable it :)

[Eric_Cartman]

i think the bridge between the cards takes care of the need for the extra bandwidth of the second slot

which is why crossfire on boards with a second slot that is only x4 only works with cards that have the bridge connections between them

[Sasqui]

i think the bridge between the cards takes care of the need for the extra bandwidth of the second slot

which is why crossfire on boards with a second slot that is only x4 only works with cards that have the bridge connections between them

That's entirely possible... even the ATI 3200 chipset in CF runs at x8 and x8 (and a third at x2 for physics)... 16 total lanes, as opposed to 20 lanes on the 965.

Even the 975 seems to have this limitation... "PCI Express x16 3 (1 electrical x16 or x8, 1 electrical x8, 1 electrical x4) " from the intel 975XBX "Badaxe"

[Zubasa]

That's entirely possible... even the ATI 3200 chipset in CF runs at x8 and x8 (and a third at x2 for physics)... 16 total lanes, as opposed to 20 lanes on the 965.

Even the 975 seems to have this limitation... "PCI Express x16 3 (1 electrical x16 or x8, 1 electrical x8, 1 electrical x4) " from the intel 975XBX "Badaxe"
Nope.:slap:
The Crossfire Xpress 3200 chipset is the first to have has dual 16x full speed PCI-E slots. (32 lanes and yes thats what 3200 stand for.)

The Crossfire Xpress 1600 chipset is the one with dual 8x bandwidth. (16 lanes)
It has the ability to switch between normal X16 mode and CF mode.

[Sasqui]

Nope.:slap:
The Crossfire Xpress 3200 chipset is the first to have has dual 16x full speed PCI-E slots. (32 lanes and yes thats what 3200 stand for.)

The Crossfire Xpress 1600 chipset is the one with dual 8x bandwidth. (16 lanes)
It has the ability to switch between normal X16 mode and CF mode.

Yep :nutkick: Unless the specs are wrong on newegg, or we're talking about something else.

PCI Express x16 3 x (2+1 Configuration: 2 Graphics + 1 Physics)
- 2 ATI CrossFire graphics cards (each operates at x8 bandwidth).
- 1 ATI Physics graphics card operates at x2 bandwidth.

http://www.newegg.com/Product/Product.aspx?Item=N82E16813136032

And from DFI:

Expansion Slots
3 PCI Express x16 slots for ATI CrossFire and ATI Physics
2+1 Configuration (2 Graphics + 1 Physics)
- 2 ATI CrossFire graphics cards (each operates at x8 bandwidth).
- 1 ATI Physics graphics card operates at x2 bandwidth.
3 PCI slots

http://www.dfi.com.tw/Product/xx_product_spec_details_r_us.jsp?PRODUCT_ID=5155&CATEGORY_TYPE=MB&SITE=NA

[Zubasa]

Yep :nutkick: Unless the specs are wrong on newegg, or we're talking about something else.

PCI Express x16 3 x (2+1 Configuration: 2 Graphics + 1 Physics)
- 2 ATI CrossFire graphics cards (each operates at x8 bandwidth).
- 1 ATI Physics graphics card operates at x2 bandwidth.

http://www.newegg.com/Product/Product.aspx?Item=N82E16813136032

And from DFI:

Expansion Slots
3 PCI Express x16 slots for ATI CrossFire and ATI Physics
2+1 Configuration (2 Graphics + 1 Physics)
- 2 ATI CrossFire graphics cards (each operates at x8 bandwidth).
- 1 ATI Physics graphics card operates at x2 bandwidth.
3 PCI slots

http://www.dfi.com.tw/Product/xx_product_spec_details_r_us.jsp?PRODUCT_ID=5155&CATEGORY_TYPE=MB&SITE=NA
Nope:nutkick:
http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_14603_14604%5E14607,00.html

AMD 580X CrossFire™ Chipset - Specifications

General

* The worlds first single chip 2x16 PCI-E chipset
* Enhanced support for over-clocking, and PCI Express performance
* Fastest multi-GPU interconnect
* Coupled with SB600 for performance

CPU Interface

* Support for all AMD CPU's: Athlon™ 64, Athlon™ 64 FX, Athlon™ 64 X2 Dual-Core, and Sempron™ processors
* Support for 64-bit extended operating systems
* Highly overclockable and robust HyperTransport™ interface

PCI Express Interface

* 2 x16 PCI Express lanes to support simultaneous operation of graphics cards
* Additional 4 PCI-E General Purpose Lanes for peripheral support
* Compliant with the PCI Express 1.0a Specifications

Power Management Features

* Fully supports ACPI states S1, S3, S4, and S5
* Support for AMD Cool『n'Quiet™ technology for crisp and quiet operation

Optimized Software Support

* Unified driver support on all ATI Radeon PCI Express discrete graphics products
* Support for Microsoft® Windows® XP, Windows® 2000, and Linux

Universal Connectivity

* A-Link Xpress II i/f to ATI northbridges; providing high bandwidth for high speed peripherals
* 10 USB 2.0 ports
* SATA Gen 2 PHY support at 3.0Ghz with E-SATA capability
* 4 ports SATA AHCI controller supports NCQ and slumber modes
* ATA 133 controller support up to UDMA mode 6 with 2 drives (disk or optical)
* TPM 1.1 and 1.2 compliant
* ASF 2.0 support for manageability control
* HPET (high precision event timer), ACPI 3.0, and AHCI support for Windows Vista
* Power management engine supporting both AMD and Intel platforms and forward compliant to MS Windows Vista
* UAA (universal audio architecture) support for High-Definition Audio and MODEM
* PCI v2.3 (up to 6 slots)
* LPC (Low Pin Count), SPI (new flash bus), and SM (System Management) bus management and arbitrations
* 「Legacy」 PC compatible functions, RTC (Real Time Clock), interrupt controller and DMA controllers

http://ati.amd.com/products/crossfirexpress3200intel/specs.html

ATI CrossFire™ Xpress 3200 (for Intel) - Specifications

CPU Interface

* Supports the Intel Pentium 4, Pentium D, Pentium Extreme Edition, Core 2 Duo, Core 2 Extreme, Celeron, Celeron D, Cedar Mill, and Allendale processors.
* Supports Front Side Bus (FSB):
o Speeds 533, 800, and 1066MHz.
o Dynamic Bus Inversion (DBI).
o Interrupt delivery.
* Intel Hyper-Threading Technology.
* In-Order Queue (IOQ) of depth 12.
* Intel Extended Memory 64 Technology (EM64T).
* Intel Execute Disable (XD) Bit Functionality.
* 34-bit host addressing.

Memory Interface

* 128-bit dual-channel DDR2 SDRAM interface.
* Supports up to 8GB of system memory.
* DDR2-400, -533, -667, -800 SDRAM.
* 256 Mbit, 512 Mbit, 1 Gbit, and 2 Gbit DDR2 DIMMs.
* Memory device widths of x8 and x16.
* Industry-standard DDR SDRAM self refresh mechanism.
* Pre-charge powerdown.
* Independent CKE and ODT signals for each memory row (total of four CKEs and ODTs per channel).

PCI Express Interface

* Compliant with the PCI Express 1.1a Specifications.
* Supports up to 3 x16 PCIE slots
* Up to six* x1 PCI Express general purpose links.
* *Note: Actual number of general purpose links available depends on the width of the A-Link Express II Interface.
* All PCI Express lanes connect directly to north bridge for maximum performance

A-Link Express II Interface

* One x4 (reducible to x2) A-Link Express II interface (PCI Express 1.1 compliant) for connection to an ATI IXP, providing more bandwidth than the older A-Link Express interface.

Software Features

* Supports Microsoft Windows 2000, XP, and Vista.
* Supports corporate manageability requirements such as DMI.
* ACPI support.
* Full Write Combining support for maximum performance of the CPU.
* Comprehensive OS and API support.
* Hot-key support (Windows ACPI 1.0b or ATI Event Handler Utility where appropriate).
* Extensive Power Management support.

Packaging

* Single chip solution in 90nm, 1.0-1.2V CMOS technology.
* 1201-FCBGA package, 35mmx35mm.

Universal Connectivity

* A-Link Xpress II i/f to ATI northbridges; providing high bandwidth for high speed peripherals
* 10 USB 2.0 ports
* SATA Gen 2 PHY support at 3.0Ghz with E-SATA capability
* 4 ports SATA AHCI controller supports NCQ and slumber modes
* ATA 133 controller support up to UDMA mode 6 with 2 drives (disk or optical)
* TPM 1.1 and 1.2 compliant
* ASF 2.0 support for manageability control
* HPET (high precision event timer), ACPI 3.0, and AHCI support for Windows Vista
* Power management engine and forward compliant to MS Windows Vista
* UAA (universal audio architecture) support for High-Definition Audio and MODEM
* PCI v2.3 (up to 6 slots)
* LPC (Low Pin Count), SPI (new flash bus), and SM (System Management) bus management and arbitrations
* 「 Legacy」 PC compatible functions, RTC (Real Time Clock), interrupt controller and DMA controllers

[Sasqui]

the AMD/ATI specs say that, but DFI couldn't make a board that meets those specs???

sorry sasqui i just dont want trouble on my boards. ya know i have a rep for that...

[Solaris17]

wow really intresting thread ftw nice find sasqui!!

[Solaris17]

not to be off topic but sasqui one day when im in manch i want to see your rig that is PIMP dude!! gotta let me over

[Sasqui]

OK - Solaris, thanks for keeping things "mild" - I'm ok with that and I've worked basically in your next home-town.

I am interested in why the DFI board has the same as the 975 limitations...

[Sasqui]

So... since no one else dug into this, and this board is beginning to reek:

Found one Intel version of the Xpress 3200 chipset, it's "2 ATI CrossFire graphics cards (each operates at x8 bandwidth)." - DFI

Three AMD versions, and yes they support (2) PCIe x16 slots. - MSI, Abit, DFI

I'll still have a Conroe... shaken, not stirred.

[wazzledoozle]

What difference does it make to tape the pins vs. adjusting the lanes in cmos?

[Zubasa]

the AMD/ATI specs say that, but DFI couldn't make a board that meets those specs???

sorry sasqui i just dont want trouble on my boards. ya know i have a rep for that...
The chipset can provide the lanes needed for X16 CF, but how they are used is up to the manufacturer.:toast:

[noneed4me2]

Does this mean my Asus A8R32 s939 board isn't true 2x16 pci/e? It took a hell of alot to get that board I could have got an CF1600(rdx200) for alot less hassle.

[tkpenalty]

No, both slots can operate at 16x simulatneously UNTIL crossfire is activated, like two X1950PROs without the bridges. Then when they are connected, the bus speed slows down.