Last month, a 4.5W Haswell derivative was spotted in an Intel datasheet. Intel formally confirmed the chip's existence today, promising to deliver the processor before the end of the year. The firm also revealed potential targets for the chip: fanless tablets and convertibles. Intel's current 6W Haswell processors require active cooling, but cutting the power consumption by 25% removes the need for a fan.
We should note that those thermal ratings refer to scenario design power, or SDP. Processors are usually tagged with TDP ratings that describe their power usage during short bursts of activity. SDP describes power draw for sustained workloads. The Intel press release doesn't quote the TDP for the 4.5W chip, but the datasheet from last month indicates that the Y-series duallie has an 11.5W thermal rating. That document also suggests that the 4.5W SDP applies only when the CPU clock is capped at 800MHz.
Intel revealed tablet-ready Ivy Bridge CPUs with 7W SDP ratings earlier this year. We haven't seen many of them in the wild, though, and it looks like the 4.5W versions of Haswell could be similarly scarce. The chips will be available in "limited volumes," according to AnandTech.
I quite like the idea of a fanless Haswell convertible, so I hope the 4.5W chips make their way into at least a few interesting systems. However, we'll probably see a lot more tablets and convertibles based on Intel's upcoming Bay Trail silicon, which is expected to power new Atom, Celeron, and Pentium processors. Leaked specifications suggest some of those Bay Trail chips will also have 4.5W SDP ratings, setting up an intriguing showdown between Intel's latest CPU architectures.