Speed-demon

Speed demon is a term which sometimes has been used to describe a CPU design which favors high clock frequencies over high . Designs described as speed demons typically employ longer pipelines, sometimes also different implementations of low-level logic, or optimizations of the manufacturing process, than most "brainiac" designs do.
Brainiac designs tend to optimize performance by having each execution step do as much as possible (using many logic levels) in order to achieve high performance at moderate clock frequencies, and also permit program branches without much penalty. Recent speed demon designs (such as Pentium 4) have instead tried to combine simpler (and thus individually faster) pipeline steps with elaborate branch prediction, as well as combining (partly) unconventional low-level logic implementations (differential signaling etc) with a refined fabrication process in order to achieve high frequencies without excessive heat production.
Examples of speed demon microprocessors include the Alpha 21064, Alpha 21164, R4000 and R4400. Later examples include the Pentium 4, especially the variant, which was designed with a 31-stage pipeline, compared to 20 stages for the variant, 12 stages for the Athlon 64, and 10 stages for the Athlon XP. Cell, POWER6 and z10 are designs from IBM that more than double the frequency through longer pipelines compared to their predecessors while not doubling the thread performance. These processors are pushing frequencies up to 5 GHz.
In a somewhat wider perspective, for certain parts of the CPU industry, one could say that the RISC strategy implied a movement from "brainiac" designs towards "speed-demon" CPUs already in the mid 1970s (although there were earlier cases of RISC-like designs). In recent years (approx. 2004-2008), the microprocessor industry has largely moved towards a strategy of more "brainiac"-like designs again, due to heat problems and other factors. The Pentium 4 was originally forecast to run at up to 10 GHz, but in reality it topped out at 3.8 GHz; both Intel's and AMD's current microprocessors are clocked below 3.8 GHz but have better performance than most Pentium 4s with higher clock rates.

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