Cannot OC memory in 1 MHz increments?

[cdub]

Hey all, I have a Gainward Golden Sample Ti4200 128MB. I am attempting to OC this beast with RivaTuner. RivaTuner allows me to make an adjustment to the memory speed in 1 MHz increments. However, in the "real" frequency display, the speed never actually increases in those increments. Instead, there are big gaps of increments. Here is a breakdown of the speeds I set and the actual reported speed (by RivaTuner):

Setting : Actual
xxx-505 : 499
506-524 : 513
525-533 : 526
534~550: 540

(I haven't actually found the upward limit of the 540 setting, but it is around 550. Likewise I haven't found the lower limit of the 499 setting.) Obviously these are stepping up in increments of 13 point something MHz, despite the speed I attempt to enter in the Tuner. I am under the impression that others are able to increment 1 MHz at a time... am I mistaken? Has anyone seen this problem? I have tried using the "low level hardware overclocking" with the same results. Any thoughts would be helpful. Thanks!

 

[BFG10K]

MHz speeds are derived from a oscillator running at some frequency and any speeds you can use are actually a multiple of that number. Therefore while the software may report 1 MHz increments, the actual clock frequency is increasing in multiples of the oscillator's frequency.

 

[cdub]

Interesting. So, do different Ti4200's have different increments (ex. mine steps in 13 point something MHz increments)? Or is it true that when someone claims to have gotten their card's memory to 550, it is actually running at 540 MHz? Does every card have a slightly different frequency?

 

[Jeff7]

I use Rivatuner, and it has a low level overclocking setting window. Well in that is a More button - changing it to Maximum accuracy will, well, increase the memory speed setting accuracy. I don't know if that will affect stability though.

 

[BFG10K]

So, do different Ti4200's have different increments (ex. mine steps in 13 point something MHz increments)?

No the oscillator will be the same in all Ti4200s. In fact, it should be the same across all video cards.

Or is it true that when someone claims to have gotten their card's memory to 550,

The number they give you will be the number reported by the drivers. However the drivers, unlike RivaTuner, don't report the true clock frequencies. So for example they might tell you they're running between 506 MHz to 524 MHz as reported by the drivers but in actual fact they're running at 513 MHz whenever they're inside that range. Of course they don't have RivaTuner so they don't see this.