28nm GCN midrange = 1024 shaders + 2GB on 256bit?

R

R3MF

[H]ard|Gawd
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What do we know about the upcoming midrange GPU's:

I heard worrying rumours of 844 shaders (or thereabouts) which screams "disabled shader units!" I personally would find this disappointing, as i hate buying tech with artificially disabled functionality. what say you?

oh, and memory, while i presume it to be 2GB on 256 bit have people heard anything different?

anything else such as a die-size or tdp?

kind regards
 
cheers.

odd that pitcairn has such a freaky number of shaders.
 
Damn, if it's going to be March by the time these come out, I might as well just go for the 7950-1.5GB or the Tahiti LE. (Or whatever Nvidia is showing by that point, if anything). Shame the early Feb birthday gift to myself wasn't meant to be... :(
 
You know what personalJ posted is completely wrong.

http://www.tomshardware.co.uk/radeon-hd-7970-benchmark-tahiti-gcn,review-32344.html

But first, we’ll share what we know about the Radeon HD 7000 series. Despite rumours to the contrary, all of the 28 nm Radeon 7000 series GPUs, previously code-named Southern Islands, are based on the Graphics Core Next architecture. That includes the Radeon HD 7700 series (Cape Verde Core), 7800 series (Pitcairn), and 7900 series (Tahiti), at the very least. AMD may include some 40 nm products under the 7000-series umbrella, and those would employ rebranded VLIW4/5 architectures.
Click to expand...
 
I don't think 844 is a correct number, since it is not equally divisible by 64 (844/64=13.1875).

There are 64 ALUs (shaders) per Compute Unit, a 'full' Tahiti has 32 CUs for 2048 shaders (32x64=2048), and AMD disables 4 CUs for each lower tier, so the procession might be like this:

7970 = 32CU/2048
7950 = 28CU/1792
24CU/1536
20CU/1280
16CU/1024
12CU/768
8CU/512
4CU/256
 
quite happy to agree with the logic, particularly that a "16CU/1024shader" chip would make a logical mid-range gpu.

and yet we get all these silly numbers..............?
 
R3MF said:
quite happy to agree with the logic, particularly that a "16CU/1024shader" chip would make a logical mid-range gpu.

and yet we get all these silly numbers..............?
Click to expand...

I'm actually hoping that either a 7870/7890/7930 ships with the 24CU/1536 shader configuration, that way we can see the differences between GCN and VLIW4.

I'm thinking, instead of a 1.5GB 7950, a 7930 with: 2560MB 320-bit GDDR5, 32 ROPs and 1536 shaders would fit nicely at $299-$349...
 
The 7890 is 1536 shaders but 384-but memory bus

EDIT: Here I made this from the info in the other thread
southernislands.png
 
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so this table obviously doesn't hold water anymore, any speculation on how many shaders the midrange gets to go with its 256bit bus?

a) 1024
b) 1536
c) some silly number due to wonky shader clusters like the 7770
 
R3MF said:
so this table obviously doesn't hold water anymore, any speculation on how many shaders the midrange gets to go with its 256bit bus?

a) 1024
b) 1536
c) some silly number due to wonky shader clusters like the 7770
Click to expand...

Well, since the 7770 only has 640 shaders (10 clusters), it kind of leads to there being either 3 or 4 7800 cards, or 3 or 4 7800s and a 7930.

Cape Verde in the 7770 is about 1/3 of Tahiti, so it is reasonable to think that the highest Pitcarin SKU could be ¾ of Tahiti:

7970: 32CU, 2048sh, 32ROPs, 128TMU
7950: 28CU, 1792sh, 32ROPs, 112TMU
If AMD creates a Tahiti LE chip;
7930: 24CU, 1536sh, 32ROPs, 96TMU
The 7890 could either be another Tahiti LE, or a Pitcarin XT;
7890: 20CU, 1280sh, 24ROPs, 80TMU
7870: 18CU, 1152sh, 24ROPs, 72TMU
7850: 16CU, 1024sh, 24ROPs, 64TMU
7830: 14CU, 896sh, 24ROPs, 56TMU
7770: 10CU, 640sh, 16ROPs, 40TMU
7750: 8CU, 512sh, 16ROPs, 32 TMU
 
I wouldn't pay too much attention when it comes to shaders. Not that moar isn't better, but look at how with a slight OC the 7950 can match the 7970 stock clocks and comes very close to its performance despite having a fewer number of shaders.

The # of shaders will certainly give a fairly good estimate to its performance, but it seems like clock speed factors in just as significantly.
 
cheers both, a 20 cluster 7890 with 1280 shaders would be a nice card however.
 
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