MIPS-X

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MIPS-X is a 32-bit RISC microprocessor and its own instruction set, developed at Stanford as a follow-up to the MIPS project. Work began in 1984 with support from DARPA, and the final design was described in 1986–87 papers. Unlike the original MIPS, MIPS-X was never sold as a general workstation CPU and mainly appeared in embedded designs based on IIT‑designed chips for digital video.

Although it was created by the same team and is architecturally similar, MIPS-X is not compatible with the main MIPS R-series. It introduced the concept of a delayed branch with two delay slots and includes a Processor Status Word (PSW) register that holds flags for interrupts and other status information.

By the mid-2000s, support for MIPS-X was scarce and mostly provided by specialist developers (for example, Green Hills Software); it is not included in GCC. MIPS-X has become notable in DVD player firmware because many low-cost players use IIT/ESS Technology chips based on this design, often with a DSP coprocessor for MPEG audio and video decoding (as in ESS VideoDrive SoCs).