A thought on 4850

[Headfoot]

So I was thinking the other day,
The 4850 is fast, but if you had to pick a bottleneck the most obvious choice would be the memory bandwidth. That is due to the choice of GDDR3 and a smaller bus width.

My question is why didn't they use GDDR4? They used it on the previous generation, and they have a mature supply of it. Also it can't be that expensive since it is used on the 3000 series and they sank to a lower price than the 4850 is now (of course memory isn't the only costly bit on a graphics card, but just for arguments' sake). The memory frequency bump should be severe enough to ease the memory bandwidth bottleneck to the point where it would be more or less equal to the power of the GPU, for a small added cost. It would then also perform better in Crossfire, (most likely) selling more units.

My current theory as to why they didnt use it would be that it is just too expensive in the greater scheme of things, but thats a totally wild guess. Any thoughts?

[Radiator]

My best guess is that they wanted to make a bigger performance difference between the HD 4870 and HD 4850 than between the HD 3870 and HD 3850 .
Also , GDDR4 = higher latency , so higher clocks = not that big of an increase of real-world performance ( correct me if I'm wrong ) .

[aliquidparadigm]

You are mostly correct, but the biggest motivating factor is the cost of the RAM.

[Die Auslese]

So does this mean a 4860 is one the horizon, with GDDR4, or maybe a cheaper 4870 with 256mb, something I don't know.

[Radiator]

256MB on a HD 4870... thats the worst thing they can do ... even 512MB is somewhat low for a card as powerful as that .

[Headfoot]

Radiator you may have hit something there on the latency issue. I suppose higher clocks would mean a whole lot of nothing if the latency is too loose on GDDR4. I am relatively unfamiliar with GDDR4. I'll give it some research and see what turns up.

EDIT:
I quote from the GDDR4 article on Wikipedia:
On the signaling front, GDDR4 expands the chip I/O buffer to 8 bits per two cycles [from GDDR3], allowing for greater sustained bandwidth during burst transmission, but at the expense of significantly increased CAS latency (CL)...

[ultima]

i saw a review with an highly overclocked 4850 (almost 4870 speeds), that was almost doing as well as a stock 4870. so to me that means the memory isn't helping or limiting it that much

sorry i'll have to go search for the review again and hopefully find it

i personally believe that the memory is just hype.
memory is already extremely fast

and i also agree that 512 mb is probably limiting the 4870

if you look at the reviews of the 4870 X2 with 2GB
on high resolutions and with increased AA it barely budges on the frame rates

while the stock 4870 starts to drop off, i would love to see a 4870 with 1GB of ram

[Radiator]

i saw a review with an highly overclocked 4850 (almost 4870 speeds), that was almost doing as well as a stock 4870. so to me that means the memory isn't helping or limiting it that much

sorry i'll have to go search for the review again and hopefully find it

i personally believe that the memory is just hype.
memory is already extremely fast

and i also agree that 512 mb is probably limiting the 4870

if you look at the reviews of the 4870 X2 with 2GB
on high resolutions and with increased AA it barely budges on the frame rates

while the stock 4870 starts to drop off, i would love to see a 4870 with 1GB of ram
That 2 GB on the HD 4870 X2 doesn't mean jack , it's still 1 GB times 2 , like in SLi/CF .
But yeah , 512MB is definitely a limiting factor... but not a huge one .

[ultima]

ya i realize it wasn't shared 2 gb of memory

however that meant 1 gb for each card

i'd still like to see a 4870 with 1 gb just to see how it fared
if it wasn't the dual card doing the work or not

[Radiator]

1GB wouldn't make a huge difference , because 512MB isn't that big of a limiting factor at the moment , but who knows what the future brings us... when new games ( Red Faction 3 , Far Cry 2 , etc. ) get released , I'd like to see the difference between a 512MB and a 1GB one aswell .

[Headfoot]

I do believe the 4870 could benefit from 1gb of memory, they choose 512 MB almost certainly from a value perspective.

Their perspective must have been that GDDR5 is expensive, and the added performance would not be worth the extra cost.

It is almost certain they will refresh the 4870 with a factory-overclocked version with 1gb of GDDR5 when the price comes down.

[Radiator]

I do believe the 4870 could benefit from 1gb of memory, they choose 512 MB almost certainly from a value perspective.

Their perspective must have been that GDDR5 is expensive, and the added performance would not be worth the extra cost.

It is almost certain they will refresh the 4870 with a factory-overclocked version with 1gb of GDDR5 when the price comes down.

At this point , it would benefit in just a couple of games , but that's temporary , it will have a larger use once those new games get released .

[Headfoot]

Im sure most of the "value" of a refresh would be the fact that its refreshed. If you can re-release the same card with larger numbers (More Ram! Higher Clocks!) you can essentially get publicity and consumer awareness for next to no additional investment in the product.