R4600

The R4600, code-named "Orion", is a microprocessor developed by Quantum Effect Design (QED) that implemented the MIPS III instruction set architecture (ISA).

The R4600 was instrumental in making the Indy successful by providing good integer performance at a competitive price.

The R4600 was a simple design; it was a scalar processor, issuing up to one instruction per cycle to its integer pipeline or floating-point unit (FPU).

Single and double precision multiplies are partially pipelined and have an eight-cycle latency and a six-cycle throughput.

The SysAD bus is 64 bits wide and can operate at clock rates up to 50 MHz for a peak bandwidth of 400 MB/s.

SGI offered a reference design in the form of the UltraP module, aimed at OEMs, permitting R4600 and R4400 processors to work in systems designed for Intel's Pentium processor by employing bus translation logic.

Subsequent versions were to offer switching between concurrently running operating systems.

It had custom instructions for improving the performance of fixed-point digital signal processing (DSP) applications.

Around the same time, Classic boxes also started being manufactured with R4640 processors from NKK instead of IDT.