How PS2 Games Work: Hardware/Software Execution Flow

The PlayStation 2 executes games through a tightly coupled hardware pipeline. Here's the lifecycle of a frame:

1. Disc → EE RAM

• DVD-ROM (4.7/8.5 GB) read by laser → **EE (Emotion Engine) Main RAM (32 MB RDRAM)** via **DMAC** (Direct Memory Access Controller).
• Game binary (ELF) + assets (textures, models, audio, scripts) loaded on demand.

2. EE (CPU) — The Brain

• Core (MIPS III, 294.912 MHz): Runs main game loop, AI, physics, scripting, input handling.
• VU0 (Vector Unit 0): Coprocessor for geometry transform/lighting (macro mode) or general SIMD.
• VU1 (Vector Unit 1): Dedicated to **vertex processing** (micro mode). Runs micro-programs (VU1 code) uploaded by EE. Parallel to EE.
• IPU (Image Processing Unit): MPEG-2 decode (FMVs), texture decompression (VQ).

3. GS (Graphics Synthesizer) — The Pixel Pusher

• 4 MB eDRAM (embedded): **Entire framebuffer + Z-buffer + texture cache on-chip.** 38.4 GB/s bandwidth (256-bit × 150 MHz).
• Pixel Fill Rate: 2.4 GP/s (16 pixels/clock × 150 MHz).
• Features: Alpha blending, depth test, stencil, fog, point sprites, bilinear/trilinear filtering. **No programmable shaders.** Fixed function.
• EE → GS via **GIF (Graphics Interface)** packet stream (DMA).

4. Audio (SPU2)

• 2× SPU cores (PS1 backward compat + new). 48 channels, ADPCM, reverb, 3D positional. 2 MB RAM.

5. IO & Peripherals

• IOP (I/O Processor): MIPS CPU (same as PS1 CPU) — runs DVD, USB, Ethernet, HDD, Memory Card, Controller (via SI/O).
• During PS2 games, IOP handles streaming from DVD, controller polling, HDD access.

6. Frame Loop (Simplified)

1. EE: Read controller (via IOP) → Update game state → Build display lists (VU1 microcode + data).
2. EE → VU1: Kick micro-program (DMA).
3. VU1: Transform vertices → Clip → Perspective divide → Send triangles to GS (via GIF).
4. GS: Rasterize → Blend → Write to eDRAM framebuffer.
5. GS → DAC (Video Encoder) → Analog Component / RGB / S-Video / Composite.
6. EE: Kick SPU2 for audio frame.

Why It Was Special

Massive on-chip bandwidth (GS eDRAM) + parallel VU1 allowed complex scenes at 60fps (480i) with zero texture memory bottleneck. The "Emotion Engine" name wasn't marketing — it was a DSP-inspired heterogeneous architecture years ahead of its time.