The MIPS architecture has several optional extensions. MIPS32/64 primarily differs from MIPS I–V by defining the privileged kernel mode System Control Coprocessor in addition to the user mode architecture. As of April 2017, the current version of MIPS is MIPS32/64 Release 6. The early MIPS architectures were 32-bit 64-bit versions were developed later. There are multiple versions of MIPS: including MIPS I, II, III, IV, and V as well as five releases of MIPS32/64 (for 32- and 64-bit implementations, respectively). MIPS ( Microprocessor without Interlocked Pipelined Stages) is a reduced instruction set computer (RISC) instruction set architecture (ISA) : A-1 : 19 developed by MIPS Computer Systems, now MIPS Technologies, based in the United States. Therefore, the R12000 and older processors are fully open. The R12000 processor has been on the market for more than 20 years and so cannot be subject to patent claims. MIPS Technologies, Imagination Technologies
