LSI Logic / Sony · 1994 · Sony PlayStation R3000A-compatible CPU with Geometry Transformation Engine
A 33.8688 MHz MIPS RISC processor paired with a dedicated geometry co-processor that did the 3D maths. The GTE is the reason the PlayStation could push hundreds of thousands of polygons a second in 1994.
The PlayStation's main processor is a MIPS R3051, a 32-bit RISC part compatible with the MIPS R3000A, running at 33.8688 MHz and rated at about 30 MIPS. It has a 4 KB instruction cache and, unusually, a 1 KB data cache configured as a scratchpad: rather than caching memory automatically, it is a small block of very fast memory that programmers fill deliberately. The system has 2 MB of main RAM. The CPU on its own would not have made the PlayStation a 3D machine. That job fell to the Geometry Transformation Engine, a co-processor on the same chip dedicated to the matrix and vector arithmetic needed to rotate, project and light 3D models. Rated at 66 MIPS, it allowed Sony to quote figures of 360,000 flat-shaded polygons per second, 180,000 texture-mapped polygons, or 90,000 with texture mapping, lighting and Gouraud shading. The GTE works in fixed-point arithmetic rather than floating point, a choice that helped speed but contributes to the wobbling, jittering vertices characteristic of PlayStation games. A third unit, the Motion Decoder (MDEC), decompresses video and images at around 80 MIPS. It made full-screen video practical on a double-speed CD-ROM drive and is why so many PlayStation games opened with lavish full-motion cut-scenes. Together the three units gave developers a machine that was straightforward to program for 3D at a time when the Saturn's competing design required juggling two CPUs.
| CPU | MIPS R3051 (R3000A-compatible), 32-bit RISC, 33.8688 MHz, ~30 MIPS |
|---|---|
| Cache | 4 KB instruction cache; 1 KB data scratchpad |
| GTE | 66 MIPS geometry co-processor |
| Polygon rates (quoted) | 360,000 flat / 180,000 textured / 90,000 textured, lit and Gouraud-shaded per second |
| MDEC | Video and image decompression, ~80 MIPS |
| Main RAM | 2 MB |