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Basically, expect 5% IPC improvements, but big power savings in a lot of ways on the same process node as Kaveri. Apparently Carrizo is due to arrive in the second quarter of this year.
The 5% IPC improvement is enough to keep pace with Intel's typical yearly improvements. Unfortunately for AMD, "keep pace with" means "remain about 30% behind". Zen can't come soon enough in that regard.
But large power savings at idle will extend battery life considerably. I don't know if AMD will catch Haswell/Broadwell there, but at least getting into the same ballpark is good enough. The difference between 0.1 W and 0.2 W matters a lot less than the difference between 1 W and 2 W--or the difference between 5 W and 10 W.
Large power savings at load mean you can do things while using less power, or you can clock the chip more aggressively. This could be a big deal for games, allowing considerable CPU turbo while the GPU is in use.
Carrizo is also an SoC, which saves a lot on both cost and power. It might be the reason why Kaveri didn't get used much in laptops: Carrizo is much better for laptops and not that many months behind.
But it also explains why Carrizo isn't coming to desktops: it would be a bad desktop chip. You don't make an SoC with 6 SATA ports and 8 USB ports. Laptops don't need that many ports. But if your entire system has only 2 SATA ports, 4 USB ports, and minimal PCI Express connectivity, it's a stupid chip for desktops.
Furthermore, there are trade-offs between high performance and low power consumption. While still a Bulldozer derivative, Carrizo goes heavily for low power consumption. That's absolutely the right choice for the laptop market that it targets, but terrible for desktops. If a desktop part could only have the CPU clock up to 3.5 GHz, even with the IPC increase, that's still slower than Kaveri or even Richland. The GPU is better than Richland, to be sure, but even if the part manages to be as fast as Kaveri in a desktop while using 30% less power, so what?
I didn't find any mention of Carrizo's PCI Express bandwidth. It's not clear to me whether there will be enough to reasonably attach a discrete video card. Broadwell, for example, doesn't have enough bandwidth for that. Nor do Bay Trail or Beema. But that's probably all right for the markets AMD is targeting with Carrizo; if you wanted a high-powered gaming laptop, you'd want an Intel CPU to go with that discrete video card.
Also important is that AMD claims that they're getting these huge gains on the same process node as before. In one sense, this leaves the status quo unchanged in the AMD versus Intel wars: AMD has better GPUs and Intel better CPUs. But AMD got their big gains without a new process node, while Intel had the biggest process node jump they had in many years. Moving to 14/16 nm should offer huge gains when AMD can do that, hopefully next year.