OCing 8800GTX - manual and factory mode - OCing 8800GTX, part 2
Author: Luka Rakamaric
Date: 08 Apr 2007

We mentioned before that not all parts of the GPU operate at this frequency. The SPs work at a much higher frequency, stock value 1350 MHz. As a part of the core, they are linked to the base frequency, so when you raise it, they will also work faster. Since Riva Tuner is capable of monitoring this GPU domain as well, it was determined that the SP clock also rises in jumps, but the interesting thing is that they do not jump at the same point the core does. Instead, these numbers show the value of base clock that triggers the SP clock change and its value.

565=1350
589=1404
611=1458
634=1512
657=1566
681=1620

You can see that using the same requested range, IE 585-603, which results in a single core clock of 594, you can actually have two SP clocks, 1350 and 1404 MHz. Since raising the SP clock only will also increase performance, the real state of things was kind of blurry for some time.

The same principle also applies when clocking the memory:
from 897 to 908 = 900
from 909 to 927 = 918
from 928 to 940 = 936
from 941 to 958 =945
from 959 to 985 = 972
from 986 to 1003 = 999
from 1004 to 1116 =1008
from 1117 to 1035 = 1026
from 1036 to 1048 = 1044
from 1049 to 1066 =1053
from 1067 to 1101 = 1080
from 1102 to 1110 = 1107

So, again, no matter what you set as a memory clock, the actual clock will be one of the values on the right.

To test this theory, we used our usual benchmarks on the following system:
- Intel Core 2 Duo E6700, 2.66 GHz
- EVGA nForce 680i SLI
- OCZ DDR2 PC2-8000, 2x1 GB
- Western Digital RaptorX 150GB
- OCZ ProXstream 1000W

The maximum clock we were able to get out of our Galaxy 8800GTX was 612/1053 MHz. We will slowly take you through this OC "procedure" - it might help you. The SPs were operating at 1458 MHz, as the requested clock was set as 616 MHz. The XO card from Point of View comes OCed, so we tested the base clocks - 600MHz for the core and 1900 MHz for the memory. We'll do a small head-to-head comparisment but include more results for the Point of View XO card due to timeframe (overnight testing of Galaxy 8800GTX). Of course, it?s pretty easy to see the correct numbers for these OC settings on XO card now - 594, 1890.

At first, we decided to only overclock the core and leave the memory at 900 MHz. We were able to go to the next level of 621 MHz, but could not raise the SP clock to 1512 MHz. So we decided to benchmark requested values of 617 MHz and 633 MHz. In all benchmarks, both frequencies scored within one percent of each other, so we can say the result is the same. Then we tried to overclock just the memory, leaving the GPU at 576 MHz. We were able to go up to 1080 MHz. Since the range of this memory clock value is from 1067 to 1101, we used those two requested frequencies to confirm the previous result. Again, the score was virtually identical, so we can say that the memory was at the same frequency in both runs.