Architectural differences between PPE and SPE SIMD support

The PPE processes SIMD operations in the VXU within its PPU. The operations are those of the Vector/SIMD Multimedia Extension instruction set.

The SPEs process SIMD operations in their SPU. The operations are those of the SPU instruction set.

The major differences between the PPE and SPE architectures are summarized in Table 1.
Table 1. PPE and SPE Architectural Comparison
Feature PPE SPE
Number of SIMD registers 32 (128-bit) 128 (128-bit)
Organization of register files separate fixed-point, floating-point, and vector registers unified
Load latency variable (cache) fixed
Addressability 2⁶⁴ bytes

256-KB local store
2⁶⁴ bytes via DMA
Instruction set more orthogonal optimized for single-precision float
Single-precision IEEE 754-1985 extended range
Doubleword no doubleword SIMD double-precision floating-point SIMD
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