Theory behind the 9500 -> 9700 mod

[diehlr]

I'm speculating here, but this is my guess about how Sapphire is able to convert a 256-bit memory bus into a "128-bit" memory bus. I am not sure if this was discussed on other websites or not. ATI has mentioned the R300 uses a crossbar memory architecture, similar to what Nvidia uses. Check out http://www.nvnews.net/previews/geforce3/lightspeed_memory.shtml for more info. My guess is the resistor is placed on Sapphire's R300 to disable 2 of the 4 memory controllers. With half of the memory controllers operating, all of the memory is still addressable (each controller can address any memory location) but with approx. half the effective bandwidth to the graphics memory, since half as many reads/writes can occur at once. By moving the jumper, you switch on the other two memory controllers and thus double the amount of available bandwidth. If you think about it, it makes sense and could be what Sapphire is using on the 128 meg 9500 boards. My guess is the central point is a chip enable, the top/bottom points are ground and VDD. The resistor is pulling the chip enable line of the memory controllers either high/low to disable the controllers.. moving it to the opposite logic state enables the controllers.

Why they would choose to use the 9700 boards with the 9500 is a different story altogether, of course..

 

[diehlr]

... or does the card always have a 256-bit bus and is simply starved for fillrate by only having 4 pipelines? I think I remember seeing some benchmarks that proved the 128 meg cards have twice the memory bandwidth of the 64 meg cards now that I think about it. I wish I could remember the URL.

 

[frustrated2]

Here is my take on the radeons

9700 and pro are 256 bit 8 pipelines

9500 and pro are 128 bit 4 pipelines

Some of the 9500 non pro versions seem to be built on a 9700 board with all of the bells and whistles there just disabled. Seems this would be way to expensive to produce. But leave it to the guys at anandtech to figure it out

 

[EdipisReks]

i'm not quite sure why everyone is so confused about this, but here is the straight dope. the 9700 series cards are built with a 256 bit memory bus. the 9500 pro, which has always had a dedicated PCB design, has the exact same chip as the 9700 but the bus has been redesigned to only be 128 bits wide. the 128 MB non-pro 9500 is built either on the 9700 board or on the 9500 pro board. those built on the 9700 board share the 256 bit bus that the 9700 has. however, the non-pro 9500's only have 4 pixel pipelines enabled to keep them from competing with more expensive boards. when you enable the 4 disabled pipelines on the 9500, you can get 2 results: if the 128 MB 9500 is built on a 9700 PCB, then you get a non-pro 9700. however, if the 128 MB 9500 is built on the dedicated 9500 board that the was designed for the 9500 pro (which all currently manufactured 9500s are on) then you get a 9500 pro.

the resistor mod only changes whether the GPU has 4 or 8 pixel pipelines enabled. it does not effect the memory bus at all. my theory as to why some sapphiretech 9500's are built on the 9700 board is this: sapphiretech had a lot of 9700 boards and they decided to use them in non-pro 9500 production in order to fill the gap until sufficient dedicated 9500 boards (which have fewer layers and are cheaper to make) could be made. the reason they didn't worry about the non-pro being too fast with the 256 bit bus is the fact that with only 4 pixel pipelines, the 128 MB 9500 cannot take advantage of the extra memory bandwidth. they never thought anyone would hack the card, so they didn't bother changing the memory bus. sapphiretech has switched to 9500 boards for all pro and 128 MB non-pro 9500's now, which they had always planned to do once production ramped up (in other words, they didn't switch because of the resistor modification), so it is difficult to find the old 9700 PCB cards. even with the new 9500 (64 or 128 MB), however, it is still possible to do the resistor mod and turn the card into the faster and more expensive 9500 pro (well, the 128 MB version is the same as the 9500 pro, and the 64 MB version is the same except for having half the RAM). if sapphiretech had waited until there were enough 9500 boards for the non-pro 9500, then they would have been introduced weeks later than they were. sapphiretech figured (correctly) that it was better to sell a product with slightly lower profit margins (due to the more expensive PCB's) than not sell any product at all.

to summarize:

9700 and 9700 pro=8 pixel pipelines and always a 256 bit wide memory bus.
9500 pro=8 pixel pipelines and always a 128 but wide memory bus.
128 MB 9500 non-pro=4 pixel pipelines and a 256 bit or 128 bit wide memory bus depending on what kind of PCB the card is built on.

THE RESISTOR MOD HAS ABSOLUTELY NOTHING TO DO WITH THE MEMORY BUS. NOTHING AT ALL. IT ONLY EFFECTS HOW MANY PIXEL PIPELINES ARE ENABLED. does that help?

[edited to remove screams of frustation]

 

[TroutFish]

This is interesting info, thanks.

I've been looking for non-pro Sapphire 9700's, but haven't found any on Pricewatch. Anyone have a source for these? I'm interested in these because supposedly they run more quietly than other 9700's.

Thanks,
TF

 

[Lizardman]

Originally posted by: TroutFish
This is interesting info, thanks.

I've been looking for non-pro Sapphire 9700's, but haven't found any on Pricewatch. Anyone have a source for these? I'm interested in these because supposedly they run more quietly than other 9700's.

Thanks,
TF

more quietly... what does that matter. I have seem some 9700's non pro on pricewatch. Why do you want the sapphire brand just get the ati branded ones.

Atlantis ver

 

[TroutFish]

Thanks for the link, LizardMan,

That's what I was looking for. Interesting, supposedly ATI was only going to build Pro versions, and leave it to their partners to build non-pro.

TF

 

[Kazuo]

The Sapphire R9500 has a 256-bit bus that's likely strangled. But I think the BIOS is what's disabling it. The resistor jumper changes it from 4 pipeline (R9500) to 8 pipeline (R9500 Pro). If you look in ATi's specs, the 9500 is not meant to have 128MB of RAM, because that gives it the 256-bit wide bus. Which is why Sapphire is screwing ATi over by going ahead and putting 128MB on it, because it's basically making their 9500s into a super-cheap 9700-class.
9500: 4 pipeline, 128-bit bus, 64MB only (except for Sapphire, who cheats)
9500 Pro: 8 pipeline, 128-bit bus on a special board, 64 or 128MB
9700: 8 pipeline, 256-bit bus, slower
9700 Pro: same as 9700 but faster RAM (and higher clocked VPU, but the same VPU nevertheless)

 

[Kazuo]

The reason someone would want a Sapphire is because Sapphire also helps ATi make their own boards. So basically you end up with a fully ATi-approved board (because it's likely the same or similar) for less. And they tend to be more creative than ATi in their board making. Sapphire rocks the boat- especially with screwing ATi and giving the R9500 a 256-bit wide bus