Several other technologies in the CPU-GPU spectrum have some features in common with it, although Ageia's product was the only complete one designed, marketed, supported, and placed within a system exclusively being a PPU.
An early academic PPU research project[1][2] named SPARTA (Simulation of Physics on A Real-Time Architecture) was carried out at Penn State[3] and University of Georgia.
It consists of a general purpose RISC core controlling an array of custom SIMD floating point VLIW processors working in local banked memories, with a switch-fabric to manage transfers between them.
[12] To compete with the PhysX PPU, an edition known as Havok FX was to take advantage of multi-GPU technology from ATI (AMD CrossFire) and NVIDIA (SLI) using existing cards to accelerate certain physics calculations.
Nonetheless GPUs are built around a larger number of longer latency, slower threads, and designed around texture and framebuffer data paths, and poor branching performance; this distinguishes them from PPUs and Cell as being less well optimized for taking over game world simulation tasks.
The Codeplay Sieve compiler supports the PPU, indicating that the Ageia physX chip would be suitable for GPGPU type tasks.
Its feature-set and placement within the system is geared toward accelerating game update tasks including physics and AI; it can offload such calculations working off its own instruction stream whilst the CPU is operating on something else.
Being a DSP however, it is much more dependent on the CPU to do useful work in a game engine, and would not be capable of implementing a full physics API, so it cannot be classed as a PPU.