A Practical Map of the Original PlayStation
The original PlayStation is a group of specialized processors connected by narrow, explicit data paths. The CPU runs game code, the GTE accelerates geometry math, the GPU draws 2D primitives, the SPU plays sound, and the CD-ROM supplies data that cannot remain in memory.
Understanding those boundaries explains most PS1 engine decisions. The machine is fast when work is prepared for the right unit and expensive when the CPU has to compensate for a poor data layout.