Question(s) about Matrox G400 architecture and DDR...

[newguy]

By now, we all know the story of the G450, how it uses a 64 bit bus hooked up to DDR RAM. We have also heard ad infinitum that a G400 vanilla will outperform it.

The G400, of course, has the the famous 256 bit dual bus architecture, which gives it power and bandwidth, (relatively speaking ) even hooked up with modest SDRAM.

The question is, why can't Matrox utilize the 256 bit dual bus with DDR? Granted, the chip was developed at a time when DDR wasn't considered as reality, let alone mainstream.

Is it simply a matter of clock speed of the chip? Since DDR RAM is sending data twice per clock cycle, it would seem that the older chip architecture possibly couldn't address it. If Matrox was able to utilize the full 256 bit capability of their design to work with DDR, I'm sure the results would be stunning. Perhaps this goes to the heart of the infamous "G800" specification.

One last question, would 64MB onboard VRAM(case of 400) or 64MB onboard DDR RAM(case of 450) help in real world scenarios? My guess is only in a certain very few applications.

[dZeus]

DDR isn't double the bandwidth in traces, but double the clockspeed. It would be _incredibly_ expensive to make a chip and/or card with a 256 bit memory interface. And btw. the G400 core and memory are very closely matched, so having twice as fast memory (DDR) would only help with a twice as fast core.

256bit Dualbus has nothing to do with the memory interface.

About your 64MB questions (and it's SDRAM/SGRAM for the G400 and SDRAM/DDR SDRAM for the G450), they won't help much, unless you want to run at insanely high resolutions that the fillrate of the card won't be sufficient for anyway, or when a game uses an insane amount of textures (which I don't think exist yet, and looking at the win2k agp texturing limitation, I wouldn't think they will appear very soon. Also DXTC/S3TC will kind of delay the need for 64MB onboard RAM I guess).

[This message has been edited by dZeus (edited 01 April 2001).]

[newguy]

Yup. It's 128 bit external bus to memory.(G400)

Thanks for the input on that dZeus, so why can't Matrox make DDR work with the current architecture?



[This message has been edited by newguy (edited 01 April 2001).]

[Guru]

[b]<FONT SIZE="+4">$$$</FONT> anyone?

No but seriously I think they decided the cards would be to expensive to manufacture!


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[dZeus]

why would they? that would mean they have to double the clockspeed of the G450 core to achieve maximum performance increase with 128 bit DDR. And obviously, it's MUCH cheaper to leave it at 64 bit, as you don't need to midify much of the G400 core for the memory interface (other than DDR support), and you only need half the amount of memory chips on the videocard itself, which saves a lot of money in the first place. And the G450 is targeted at business use, for which money is much bigger of an issue than 3d performance.