Apple iPhone 4S: Thoroughly Reviewed

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• doobydoo - Friday, December 2, 2011 - link

  Its still absolute nonsense to claim that the iPhone 4S can only use '2x' the power when it has available power of 7x.
  
  Not only does the iPhone 4s support wireless streaming to TV's, making performance very important, there are also games ALREADY out which require this kind of GPU in order to run fast on the superior resolution of the iPhone 4S.
  
  Not only that, but you failed to take into account the typical life-cycle of iPhones - this phone has to be capable of performing well for around a year.
  
  The bottom line is that Apple really got one over all Android manufacturers with the GPU in the iPhone 4S - it's the best there is, in any phone, full stop. Trying to turn that into a criticism is outrageous.

• PeteH - Tuesday, November 1, 2011 - link

  Actually it is about the architecture. How GPU performance scales with size is in large part dictated by the GPU architecture, and Imagination's architecture scales better than the other solutions.

• loganin - Tuesday, November 1, 2011 - link

  And I showed it above Apple's chip isn't larger than Samsung's.

• PeteH - Tuesday, November 1, 2011 - link

  But chip size isn't relevant, only GPU size is.
  
  All I'm pointing out is that not all GPU architectures scale equivalently with size.

• loganin - Tuesday, November 1, 2011 - link

  But you're comparing two different architectures here, not two carrying the same architecture so the scalability doesn't really matter. Also is Samsung's GPU significantly smaller than A5's?
  
  Now we've discussed back and forth about nothing, you can see the problem with Lucian's argument. It was simply an attempt to make Apple look bad and the technical correctness didn't really matter.

• PeteH - Tuesday, November 1, 2011 - link

  What I'm saying is that Lucian's assertion, that the A5's GPU is faster because it's bigger, ignores the fact that not all GPU architectures scale the same way with size. A GPU of the same size but with a different architecture would have worse performance because of this.
  
  Put simply architecture matters. You can't just throw silicon at a performance problem to fix it.

• metafor - Tuesday, November 1, 2011 - link

  Well, you can. But it might be more efficient not to. At least with GPU's, putting two in there will pretty much double your performance on GPU-limited tasks.
  
  This is true of desktops (SLI) as well as mobile.
  
  Certain architectures are more area-efficient. But the point is, if all you care about is performance and can eat the die-area, you can just shove another GPU in there.
  
  The same can't be said of CPU tasks, for example.

• PeteH - Tuesday, November 1, 2011 - link

  I should have been clearer. You can always throw area at the problem, but the architecture dictates how much area is needed to add the desired performance, even on GPUs.
  
  Compare the GeForce and the SGX architectures. The GeForce provides an equal number of vertex and pixel shader cores, and thus can only achieve theoretical maximum performance if it gets an even mix of vertex and pixel shader operations. The SGX on the other hand provides general purpose cores that work can do either vertex or pixel shader operations.
  
  This means that as the SGX adds cores it's performance scales linearly under all scenarios, while the GeForce (which adds a vertex and a pixel shader core as a pair) gains only half the benefit under some conditions. Put simply, if a GeForce core is limited by the number of pixel shader cores available, the addition of a vertex shader core adds no benefit.
  
  Throwing enough core pairs onto silicon will give you the performance you need, but not as efficiently as general purpose cores would. Of course a general purpose core architecture will be bigger, but that's a separate discussion.

• metafor - Tuesday, November 1, 2011 - link

  I think you need to check your math. If you double the number of cores in a Geforce, you'll still gain 2x the relative performance.
  
  Double is a multiplier, not an adder.
  
  If a task was vertex-shader bound before, doubling the number of vertex-shaders (which comes with doubling the number of cores) will improve performance by 100%.
  
  Of course, in the case of 543MP2, we're not just talking about doubling computational cores.
  
  It's literally 2 GPU's (I don't think much is shared, maybe the various caches).
  
  Think SLI but on silicon.
  
  If you put 2 Geforce GPU's on a single die, the effect will be the same: double the performance for double the area.
  
  Architecture dictates the perf/GPU. That doesn't mean you can't simply double it at any time to get double the performance.

• PeteH - Tuesday, November 1, 2011 - link

  But I'm not talking about relative performance, I'm talking about performance per unit area added. When bound by one operation adding a core that supports a different operation is wasted space.
  
  So yes, doubling space always doubles relative performance, but adding 20 square millimeters means different things to the performance of different architectures.