radeon 8500 128ddr overclocking?

[CSaddict]

I have a Radeon 8500 128 DDR and I have downloaded powerstripe. It lists my speeds at default as 275 core and 275 memory? This card is supposed to be 550 memory? Do I not understand how this works? What is a good speed to use?

 

[elysium]

I'm 80% sure of this, tell me if I'm wrong.

The DDR memory doubles the refresh rate. The ram runs at 275, but becous it is ddr it refreshed two times in the same cuclys, in and out. Times the speed 2 and you will get 550.

Ely

 

[CSaddict]

That makes sense. Thanks for the input.

 

[nicspits]

The advertising works like this, we'll say 550mhz because it sounds big. When it is really 275 DDR which is effectively 550mhz. that is why you'll see AMd processors with 266(133x2) FSB.

 

[CrackedSKull]

OK this my best understanding of ddr-

MHz is a frequency, so it is based on a sine curve, so it has a creast/peak and a trench/base or whatever you want to call it.

Since it is only positive half the time, you can double it by sending a second signal offseted by one half of a wavelength. So that when one wave is positive the other is negative, and vise versa.

If you don't know what a sine curve is just think of waves in water.

If anyone knows anything otherwise, please let me know.

 

[nicspits]

Ok I'll explain the whole thing in detail so at least one more person knows.

Cracked skull was mostly right. It transmits on the sign curve but regular SDR transmits data on the High and the low. DDR can do it at the High Low, and "mid" or 0 value of the curve. A complete sign curve is like an S sideways. So imagine hitting at not just the fattest parts of the S but also the tips. (the font does not display this well.) It also breaks in the center I believe making that two for SDRAM and 4 for DDR in a complete sign curve.

Mhz is measured at how close together each S is to the following one. (pretty sure, it also might be how high the fat parts stretch from the baseline but doubt it.)

Therefor when they say that it runs at 275MHZ they are not lying. When they say that it runs at 550MHZ they mean equivalently.

 

[CrackedSKull]

cool thanks, good info.

 

[Bobby_Mac]

Interesting

MHz is just the time it takes to complete one sine wave.
So to convert a Mhz rating into seconds just invert the MHz rating and that how long it takes to complete one cycle this is measure in seconds. 1Hz = 1 second
so 275MHz is like 3.363636...... nano seconds But because it is DDR it doubles so 550MHz
Im not quite certain but in electronics class they say its DDR because the clock trigger uses both negative and positive edge triggers.
Because sdram is only triggered on the positive edge or the negative edge its slower, and I believe it only uses 1 JK flipflop
DDR uses Both edges of the clock positive and negative so it performs as double SDRAM so hence the DDR. This uses 2 JK flipflops so it can use both edges of the clock.
I'll try to find a link to show a picture of what the difference it between the 2

 

[Bobby_Mac]

here we go

http://www.tricn.com/news/EDNMag_DDRsdram_090299.pdf
Here is a link that shows how DDR works

 

[elysium]

This certenly evolved into an interresting read. I was not able to see the .pdf file you added, but perhaps I will on another computer. Anyway, for the questions the thread starter asked:

Well, all cards are different, so there are no standard for what you can reach, but a 300mhz memory (equilant to 600mhz) would be reasoneble, since most the tests of radeon 8500 cards I have seen has been able to reach that speed. Just raise the speed with 5mhz each time or so.

You might want to use powerstrip for this. Search for it at download.com.

This is the most used program for oc'ing, but you might also take a look at Radeon Tweaker, who I assume you would find at the same place. This program is used to optimize your radeon card.

Wish I had a video card like that....

Ely