MIPS R4000 processors
The R4000 series, released in 1991, extended the MIPS instruction set to a full 64-bit architecture, moved the FPU onto the main die to create a single-chip system, and operated at a radically high internal clock speed (it was introduced at 100MHz). However, in order to achieve the clock speed the caches were reduced to 8KB each and took three cycles to access. The high operating frequencies were achieved through the technique of deep pipelining (called super-pipelining at the time). With the introduction of the R4000 a number of improved versions soon followed, including the R4400 of 1993 which included 16KB caches, largely bug-free 64-bit operation, and a controller for another 1MB external (level 2) cache.
MIPS, now a division of SGI called MTI, designed the lower-cost R4200, and later the even lower cost R4300, which was the R4200 with a 32-bit external bus. The Nintendo 64 used a NEC VR4300 CPU that was based upon the low-cost MIPS R4300i.
Quantum Effect Devices (QED), a separate company started by refugees from MIPS, designed the R4600 "Orion", the R4700 "Orion", the R4650 and the R5000. Where the R4000 had pushed clock frequency and sacrificed cache capacity, the QED designs emphasized large caches which could be accessed in just two cycles and efficient use of silicon area. The R4600 and R4700 were used in low-cost versions of the SGI Indy workstation as well as the first MIPS based Cisco routers, such as the 36x0 and 7x00-series routers. The R4650 was used in the original WebTV set-top boxes (now Microsoft TV). The R5000 FPU had more flexible single precision floating-point scheduling than the R4000, and as a result, R5000-based SGI Indys had much better graphics performance than similarly clocked R4400 Indys with the same graphics hardware. SGI gave the old graphics board a new name when it was combined with R5000 in order to emphasize the improvement. QED later designed the RM7000 and RM9000 family of devices for embedded markets like networking and laser printers. QED was acquired by the semiconductor manufacturer PMC-Sierra in August 2000, the latter company continuing to invest in the MIPS architecture.
Source: Wikipedia, the free encyclopedia.