vcard RAM question

[morgash]

ok so i started wondering about this the other day and maybe some of u can help me out. the list is as follows.

7900GTX: 1.1ns
7900GT: 1.4ns
7800gtx:1.6ns
7800gt:1.6ns
x1900xt/x: 1.1ns
x1800xt: 1.2ns
x1800xl: 1.4ns

so...the question is this.
x1800xl's are notoriously bad at mem overclocks. GREAT for core but the mem never quite gets where it should. If it is, in fact, 1.4ns RAM like the 7900gt, why then can a x1800xl not easily reach RAM speeds of the x1800xt. the 7900gt reaches 1700mhz with no problems, no volt mod needed. Do a graphite mod and poof u have 2.0ghz on the RAM. For that matter, i havnt seen many if any x1800xt's go that high on the memory either. whats the deal? any enlightenment on this subject would be much appreciated.

Morgash

 

[morgash]

ttt

 

[shabby]

Maybe the memory on nvidia cards gets more voltage?

 

[morgash]

perhaps. but then why would ATI do that? knowing that clock speeds influence buyers (even the best of us) why not push the RAM as hard as is safe. Even voltmodded a x1800xl cant reach mem clocks anywhere near a 7900gt. still wondering...

 

[BrownTown]

maybe ATI uses tighter timmings on its memmory so they can't run at such high speeds? Or it could just be that the RAM chips NVDIA uses are jsut good overclockers and can go over their spec alot mroe than ATIs memmories. Personally I don't like comparing synthetic numbers in non-equivilent produce lines, I just care which one is better, not which one has higher clockspeeds.

 

[morgash]

bump for more info

 

[kpb]

There are a few things that could influence that.

Memory controller- The memory controller is built into either chip and designed by the corisponding company. Obviously these are different and could definitely effect the max memory speed achievable. The memory controller in the 7900 gt is obviously designed to handle the speeds all the way up to the speeds that the speeds the gtx runs at. The 1800 only ever had to run at the speed of the 1800xt. A memory controller running within designed speeds is obviously going to have better chances than one running beyond it's designed speed.

PCB layout- The design of the board it's self can effect this too. The exact paths the memory takes. How close the tolerances are on the memory paths etc all effect this. Once again the 7900gt seems to share a board design with the 7900gtx which is designed to run at those speeds and the main difference between the 2 seems to be the cooler and the voltages on memory and core. I don't think the 1800xl shares the same board as the 1900xtx.

Over all it doesn't really surprise me that the 7900gt overclocks well considering the huge simularities with the 7900 gtx.

 

[inveterate]

f00k ati.
I won't buy their stuff till they institut the awsome Step up program.

 

[bmx045]

I just got the sapphire 1800xt, 625/1500 clocking, I aint worried! If the xl's are notorious for their lack of overclockability on the memory side, there's a good chance different brands of the 1800xt have different brand of memory modules. Different brands tell a long story about overclockability.