I'll take issue with this statement. Why would removing the T unit do anything but decrease the size of the ALUs?
Because you can't just "remove" the T unit without somehow compensating for its specific functionality?
Nevertheless, I have to correct myself with respect to the "Charlie himself said that a cluster of 4 NI shaders is about as big as a cluster of 5 EG shaders" statement. I somehow got that mixed up.
In fact, Charlie just
said that each individual NI shader should be somewhat bigger than each individial Evergreen shader.
Still, let's just say that, according to a very rough rule of thumb, 1/3 of Juniper should be shaders. Then just adding 20% more of the same shaders (800 -> 960) would add about ~ 11mm² of die space. Factor in that the "new" shaders are, shader-for-shader, somewhat more complex and (thus) bigger - and die size should grow even more: According to charlies "A group of 4 NI shaders is smaller than a group of 5 EG shaders", the upper limit of increase would be <25%, but let's just go with an assumed 10% increase in the size of each individual shader for the sake of this rough guesstimation here. Then 166mm²/3*1.2 (minimum increase in shader count)*1.1 (conservative assumption for the increase in individual shader-size) gives you ~ 73mm², i.e. an 18mm² increase over the assumed ~ 55mm² of die space devoted to shaders assumed for Juniper.
So the new shader-design alone would put Barts @ 184mm. That'd leave 16mm² for
(a) the rumored doubling of ROPs
(b) the (practically confirmed) doubling of the memory interface
(c) the rumored 60% increase in TMU count (40 -> 64)
(d) the direly needed optimizations in tesselation performance
Even presupposing that they will most probably save some die space due to expected die space optimizations, I still personally don't see how (a) to (d) could be pulled off within a <200mm² die size budget.
And finally:
If they actually managed to apply a few magic tricks to
really achieve this miracle, that would indeed be
most impressive from a sheer perf/mm² perspective - but it would also make me wonder why a Barts chip only slightly bigger than Juniper (1) had to be branded 68** after all (I'm really in favor of companies improving on their profits, but there's a difference between improving on you profits and becoming greedy) and (2) why such a rather small chip would still draw ~ 50% more power than Juniper (cf. the rumored >150W) ...
Now, I know that even neliz (whom I respect even more than Charlie) hinted at something like "GTX 470 performance @ 1/3 of the die size" a few pages earlier in this thread - but that just
(a) seems too good to be true and
(b) would really make me wonder how <200mm² could honestly be marketed as the new "sweet spot"?
(c) how many AMD engineers sold their souls to the perf/mm² devil to actually achieve (at least) HD 5850 performance @ just 60% of Cypress' die size?