The PPU is a 64-bit dual-threaded in-order PowerPC 2.02 microprocessor core designed by IBM for use primarily in the game consoles PlayStation 3 and Xbox 360, but has also found applications in high performance computing in supercomputers such as the record setting IBM Roadrunner.
The PPU is used as a main CPU core in three different processor designs: The PPU is an in-order processor, but it has some unique traits which allow it to achieve some benefits of out-of-order execution without expensive re-ordering hardware.
The instruction delay pipeline is used for the Out-Of-Order Load/Stores: cache misses are put there while it moves on.
The PPU is enhanced in the PowerXCell 8i processor to be able to make single cycle double precision floating point operations, tailored for high performance computing in supercomputers.
The VMX unit in the XCPU in the Xbox 360 is enhanced with 128 registers and is not entirely compatible with regular AltiVec.