MIPS (Microprocessor without Interlocked Pipelined Stages) is a reduced instruction set computer (RISC) instruction set architecture (ISA) developed by MIPS Computer Systems, now MIPS Technologies, based in the United States. 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). The early MIPS architectures were 32-bit only; 64-bit versions were developed later. As of April 2017, the current version of MIPS is MIPS32/64 Release 6. MIPS32/64 primarily differs from MIPS I–V by defining the privileged kernel mode System Control Coprocessor in addition to the user mode architecture. Computer architecture courses in universities and technical schools often study the MIPS architecture. The architecture greatly influenced later RISC architectures such as Alpha. As of April 2017, MIPS processors are used in embedded systems such as residential gateways and routers. Originally, MIPS was designed for general-purpose computing. During the 1980s and 1990s, MIPS processors for personal, workstation, and server computers were used by many companies such as Digital Equipment Corporation, MIPS Computer Systems, NEC, Pyramid Technology, SiCortex, Siemens Nixdorf, Silicon Graphics, and Tandem Computers. Historically, video game consoles such as the Nintendo 64, Sony PlayStation, PlayStation 2, and PlayStation Portable used MIPS processors. MIPS processors also used to be popular in supercomputers during the 1990s, but all such systems have dropped off the TOP500 list. These uses were complemented by embedded applications at first, but during the 1990s, MIPS became a major presence in the embedded processor market, and by the 2000s, most MIPS processors were for these applications. In the mid- to late-1990s, it was estimated that one in three RISC microprocessors produced was a MIPS processor. MIPS is a modular architecture supporting up to four coprocessors (CP0/1/2/3). In MIPS terminology, CP0 is the System Control Coprocessor (an essential part of the processor that is implementation-defined in MIPS I–V), CP1 is an optional floating-point unit (FPU) and CP2/3 are optional implementation-defined coprocessors (MIPS III removed CP3 and reused its opcodes for other purposes). For example, in the PlayStation video game console, CP2 is the Geometry Transformation Engine (GTE), which accelerates the processing of geometry in 3D computer graphics. The MIPS architecture has several optional extensions. MIPS-3D which is a simple set of floating-point SIMD instructions dedicated to common 3D tasks, MDMX (MaDMaX) which is a more extensive integer SIMD instruction set using the 64-bit floating-point registers, MIPS16e which adds compression to the instruction stream to make programs take up less room, and MIPS MT, which adds multithreading capability. In December 2018, Wave Computing, the new owner of the MIPS architecture (see MIPS Technologies), announced that MIPS ISA would be open-sourced in a program dubbed the MIPS Open initiative. The program was intended to open up access to the most recent versions of both the 32-bit and 64-bit designs making them available without any licensing or royalty fees as well as granting participants licenses to existing MIPS patents.. In March 2019, one version of the architecture was made available under a royalty-free license, but later that year the program was shut down again .