Overclocking 8800GTX Locking Tables - Overclock.net

DuckieHo · 04-14-07

http://it-review.net/index.php?optio...1&limitstart=0

Quote:

The heart of the 8800GTX is a G80 GPU, the first 'next generation' chip supporting DX10 and using a completely different architecture than its predecessors. NVIDIA has implemented so called unified shader architecture, meaning that there are no more pixel, vertex or geometry shaders, but only one type of shader that can do all those things. This was done with DX10 in mind, this is the first API to fully take advantage of this architecture. The G80 has 128 such simple processors, or SPs, that are clocked much higher than the rest of the GPU. We have had examples of different regions of the core operating at different frequencies in the past. In the G80, SPs operate at a stock value of 1350 MHz, which is more then twice the speed of the GPU itself, clocked at 575 MHz. The G80 in 8800GTX has a frame buffer size of 768 MB DDR3 memory operating at a stock 900 MHz. So, what happens when you overclock your card? Most utilities, including nTune from NVIDIA, will offer you +1 MHz increments on both the core clock and the memory clock. No problem you say, raise the clock from 575 MHz to a round number of 600, get some performance increase, and go to bed happy.

Recently we got some information from our friends at TheTechRepository that this is not what actually happens. VGA card chip has a frequency oscillator that determines its clock, and in the case of G80, it can’t change the clock by just 1 MHz. Through a method of trial and error while thinking about crazy multipliers that might have something to do with this, it was determined that the core clock will jump in discreet jumps rather than by what you set as an actual core clock. The following numbers show what clock the core is actually operating at when you select a value in the OC application. It was created using SysTool for OC and RivaTuner, which was showing the actual clocks in its Hardware monitor page.

from 554 to 571 = 567
from 572 to 584 = 576
from 585 to 603 = 594
from 604 to 616 = 612
from 617 to 634 = 621
from 635 to 661 = 648
from 662 to ??? = 675

So we can see that when you set your core to 600 MHz, it actually works at 594, which is exactly one percent less than what you requested.

Mhill2029 · 04-15-07

+Rep for you for this info....now that is interesting...

USFORCES · 04-15-07

I found this over on another forum it goes along with your post.

Quote:

So, an input core speed of 660(which I was running) actually had me running at a reported core speed of 648! Once I bumped it up to 662, my reported core speed jumped up to 675!! earlier I was hitting a brick wall at 665, apparently this is when the shader clock goes up another step!! So my stability issue was the shader not being stable above 1512. I created a spreadsheet to show what clocks did what for me:

It was posted by a guy over at NVNews, his name is NoiR. I can't help but to notice how similar the results are!

So, with all of that being said, I will no longer oveclock in flat amounts! I didn't even mess with 661-664 core speed too much because if I couldn't have 665, I wanted the nice round number of 660. Unknown to me, that was cheating me out of 27MHZ on the core! lol.

Anyways, my new stable speeds are 675 core and 1008(2016) memory and 1512 shader!

**Mootsfox** · 04-15-07

That would explain the 680mhz problem with the cores.

Pinhead-227 · 04-15-07

I know we wouldn't be able to get around the core clock discrepancies, but what about the core vs shader clocks? In other words, would editing the BIOS to 635/1458/1900 actually give me these clock speeds? And if not, how do I "see" my resultant speeds (in Windows Vista)?

**ENTERPRISE** · 04-15-07

Very interesting. Nice find.

OCZedd · 04-15-07

So you are saying that there is no performance difference between running your core at 661Mhz and 635Mhz?

**Mootsfox** · 04-15-07

Quote:

Originally Posted by OCZedd

So you are saying that there is no performance difference between running your core at 661Mhz and 635Mhz?

There will be, because of the shader core being higher. There will be no difference between 650 and 661 though.

OCZedd · 04-15-07

But:

Quote:

Originally Posted by DuckieHo

from 635 to 661 = 648

Although it seems that people are stating different frequncies change the shader and true core clocks.

Thats probably why manufactors of cards, like eVGA and BFG have some weird OC numbers.

**Mootsfox** · 04-15-07

Read:

635-641 = 1458 shader/648 core
642-661 = 1512 shader/648 core

The core speed will be the same, but the shaders are clocked higher, so you will see a difference.

04-15-07	#6 (permalink)
ENTERPRISE FEELING FULL OF WIN Join Date: Oct 2004 Location: Norfolk,UK Posts: 43,793 FAQs Submitted: 11 Folding Team Rank: 574 Hardware Reviews: 16 Trader Rating: 15	Very interesting. Nice find. __________________ Be friendly and polite to your fellow OCN members ! Eco Friendly Folding Please lets all FOLD for eachother!. Lets Unite! Fold For The Cause ! Fold For The People LIGHT PREVAILS For Sale:[Global]: Various Games For Sale:[Global] ENTERPRISE'S Clear out sale. For Sale:[Global] 2X 2GB Kits DDR2 RAM

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Overclocking 8800GTX Locking Tables

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