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[SOLVED]PCI-E memory bandwidth problem?

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May 9, 2011
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Motherboard
GA-Z68X-UD4-B3 BIOS:F10
CPU
Intel Core i5-2500K @ 4.8GHz
Graphics
XFX Radeon HD 6870 Dual Fan Edition
Mac
  1. iMac
Classic Mac
  1. 0
Mobile Phone
  1. iOS
ok,
so i have a gigabyte GA-Z68X-UD4(as stated in the signature), and its a dual boot with windows 7 and mac os x lion 10.7.2, i also have a XFX 687A-ZDFC AMD Radeon HD 6870 graphics card currently installed in the top pcie slot. when i open up GPU-Z, it shows that the video card supports pcie 16x at v2.0, but it's currently running at pcie 8x at v2.0. it's really weird because i dont have anything plugged into the second pcie 16x slot, so i went to gigabyte's website to check this.

1 x PCI Express x16 slot, running at x16 (PCIEX16)
* For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot.
1 x PCI Express x16 slot, running at x8 (PCIEX8) * The PCIEX8 slot shares bandwidth with the PCIEX16 slot. When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode.

so apparently, if i only have 1 pcie card(my video card) in the top pcie express 16x slot, then it should opperate at 16x, but GPU-Z says it's at 8x... is there anyway to disable the second pcie slot so that i run at 16x?

(my init display first in bios is set to pcie 16x)

i've attached a screenshot of GPU-Z


EDIT: ok, so apparantly CPU-Z says the same thing too!

i've also attached a screenshot of CPU-Z

EDIT 2: ok, so I went into Lion, and apparantly system profiler tells me the same thing

i've also attached a screenshot of system profiler

SOLVED: the problem was with the BCLK frequency, when it is disabled and at stock, it is 100MHz in the BIOS, but it actually runs at 99.70 MHz, and apparently, PCIe x16 requires BCLK to run at 100MHz at all times, so I went into the BIOS, and changed the BCLK control to Enabled and set it to 1003 instead of 1000, giving me a stable 100.1 MHz in both OS and I now have PCIe x16 speed!!!
 

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EDIT 2: ok, so I went into Lion, and apparantly system profiler tells me the same thing

i've also attached a screenshot of system profiler

SOLVED: the problem was with the BCLK frequency, when it is disabled and at stock, it is 100MHz in the BIOS, but it actually runs at 99.70 MHz, and apparently, PCIe x16 requires BCLK to run at 100MHz at all times, so I went into the BIOS, and changed the BCLK control to Enabled and set it to 1003 instead of 1000, giving me a stable 100.1 MHz in both OS and I now have PCIe x16 speed!!!

Very Nice!!! great tip! hours was trying to enable PCI-e 16x in nVidia GTX550 Ti, worked 100%! :D

Hardware
Lion 10.7.3 with DSDT tony
I7 2600K
GA-P67X-UD3-B3 Bios F7
SSD Corsair Nova 60Gb
8Gb Corsair Vengeance
1.5Tb Seagate 6.0Gbps
DVD-rW LG H20
PowerSupply Corsair CX600 Watts
Nvidia GTX550 Ti

FULL 100% Lion 10.7.3 :headbang:
 
RAT_CODE said:
EDIT 2: ok, so I went into Lion, and apparantly system profiler tells me the same thing

i've also attached a screenshot of system profiler

SOLVED: the problem was with the BCLK frequency, when it is disabled and at stock, it is 100MHz in the BIOS, but it actually runs at 99.70 MHz, and apparently, PCIe x16 requires BCLK to run at 100MHz at all times, so I went into the BIOS, and changed the BCLK control to Enabled and set it to 1003 instead of 1000, giving me a stable 100.1 MHz in both OS and I now have PCIe x16 speed!!!

Very Nice!!! great tip! hours was trying to enable PCI-e 16x in nVidia GTX550 Ti, worked 100%! :D

Hardware
Lion 10.7.3 with DSDT tony
I7 2600K
GA-P67X-UD3-B3 Bios F7
SSD Corsair Nova 60Gb
8Gb Corsair Vengeance
1.5Tb Seagate 6.0Gbps
DVD-rW LG H20
PowerSupply Corsair CX600 Watts
Nvidia GTX550 Ti

FULL 100% Lion 10.7.3 :headbang:

glad to hear it worked! :headbang: :thumbup:
 
3770k
ud5h
550ti 1gb

Tried this and it made my wifi card stop working and still showed x8 in profiler. Any ideas?
 
Djarum02 said:
3770k
ud5h
550ti 1gb

Tried this and it made my wifi card stop working and still showed x8 in profiler. Any ideas?

Ivy... the thing is, not a lot of people fully understand them yet. sorry buddy. the one thing is, why did it make your wifi card stop working... did you try turning it back to default to see if it still works?
 
hackintosh1997 said:
Djarum02 said:
3770k
ud5h
550ti 1gb

Tried this and it made my wifi card stop working and still showed x8 in profiler. Any ideas?

Ivy... the thing is, not a lot of people fully understand them yet. sorry buddy. the one thing is, why did it make your wifi card stop working... did you try turning it back to default to see if it still works?

When reverted it went back to working just fine. Long story short

Before change (was running optimized defaults) Wifi worked x8 card shows as 1.5gb instead of 1.0gb

After Change (bumped to 100.3 // above 100 in Bios shown in top right) Wifi stops, still shows as x8 and 1.5gb.

Revert (OD in Bios) it went back to the 97.33 or whatever, Wifi works, stil shows x8 1.5gb.
 
Djarum02 said:
hackintosh1997 said:
Djarum02 said:
3770k
ud5h
550ti 1gb

Tried this and it made my wifi card stop working and still showed x8 in profiler. Any ideas?

Ivy... the thing is, not a lot of people fully understand them yet. sorry buddy. the one thing is, why did it make your wifi card stop working... did you try turning it back to default to see if it still works?

When reverted it went back to working just fine. Long story short

Before change (was running optimized defaults) Wifi worked x8 card shows as 1.5gb instead of 1.0gb

After Change (bumped to 100.3 // above 100 in Bios shown in top right) Wifi stops, still shows as x8 and 1.5gb.

Revert (OD in Bios) it went back to the 97.33 or whatever, Wifi works, stil shows x8 1.5gb.


so wait. let me get this straight. you have a 550ti on the first pcie slot and a wifi card in the second pcie slot? if so, then the x16 bandwidth will be shared and become x8 and x8 for both. that cannot be changed.
 
i also remember hearing that if USB3 in bios was set to turbo mode or something (there should be an option in the BIOS) that it might cut down your PCIE bandwidth in half on Gigabyte Z68 boards.
 
SG- said:
i also remember hearing that if USB3 in bios was set to turbo mode or something (there should be an option in the BIOS) that it might cut down your PCIE bandwidth in half on Gigabyte Z68 boards.

really? I've got USB 3.0 enabled, it works, and i still have PCIE16x. I never heard of that, but I can't confirm that it's false though. one thing is, USB 3.0 on most boards (aside from z77) should be running from a third party chipset, the EJ168 in my case. I don't think that this has to do with the PCIE16X bandwidths. I could be wrong though. we learn everyday :thumbup:
 
hackintosh1997 said:
so wait. let me get this straight. you have a 550ti on the first pcie slot and a wifi card in the second pcie slot? if so, then the x16 bandwidth will be shared and become x8 and x8 for both. that cannot be changed.

No the WiFi card is like in the 5th or 6th slot at the bottom.

I will try to disable usb 3.0 and see if that fixes it. bbiab.
 
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