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MIPS architecture

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MIPS is a family of instruction set architectures, or ISAs. An ISA is a set of rules that tells a computer processor how to follow commands. MIPS belongs to a group called Reduced Instruction Set Computer, or RISC. This design philosophy focuses on using a small set of simple, efficient instructions. MIPS was developed by MIPS Computer Systems, which later became MIPS Technologies, Inc. This architecture has been essential in teaching how computer hardware and software work together. It even influenced other famous RISC designs, such as the Alpha architecture.

At its core, MIPS uses a load/store architecture. This means the processor only moves data between memory and its internal registers using specific load and store commands. All other mathematical or logical operations happen directly between the registers. The architecture is modular and supports up to four coprocessors, which are specialized helper units. COP0 is the System Control Coprocessor, which is an essential part of the processor. COP1 is an optional floating-point unit, or FPU, used for complex math. Other coprocessors, like COP2 or COP3, can be used for specific tasks. For example, the PlayStation used a COP2 called the Geometry Transformation Engine to speed up 3D graphics.

To understand how MIPS works, we must look at its registers. A register is a very fast storage spot inside the chip. The MIPS I version has thirty-two 32-bit general-purpose registers. One special register is hardwired to zero, meaning its value can never change. There are also special HI and LO registers used for integer multiplication and division. Instructions in MIPS are divided into three main types: R, I, and J. R-type instructions involve three registers and a function field. I-type instructions use two registers and a 16-bit immediate value, which is a constant number. J-type instructions use a 26-bit jump target to move the program to a new location.

The history of MIPS began in 1985. The first version was designed for the R2000 microprocessor. In 1989, the R6000 microprocessor was released as the first MIPS II implementation. While it was designed for servers, it was actually a commercial failure. In 1991, the MIPS III architecture arrived with the R4000 microprocessor. This version was used in workstations, servers, and even supercomputers. MIPS companies also tried to create the Advanced Computing Environment, or ACE, to make MIPS the standard for personal computers. While ACE did not succeed in the home market, the R4000 became very successful in professional workstations.

MIPS has been part of many famous machines. A derivative of the R4300i processor was used in the Nintendo 64 game console. Another derivative, the R5900, powered the Sony PlayStation 2. In 1994, the R8000 chipset was released for high-end scientific workstations. This chipset was important for tasks involving large floating-point workloads. In 1996, MIPS V was announced to help with 3D graphics transformations. Although MIPS V implementations were never officially introduced, its features were kept in the MIPS64 Release 1 version. This version used a feature called Paired-Single to handle math.

As the technology evolved, the architecture changed its structure. Originally, each new version was a "superset," meaning it included everything from the previous version. Engineers found this caused problems, so they changed the design. In 1999, they introduced MIPS32 and MIPS64 as distinct architectures. MIPS32 is based on MIPS II but includes features from later versions. MIPS64 is based on the MIPS V design. Interestingly, the company skipped "Release 4" of their updates. They did this because the number four is considered unlucky in many Asian cultures. As of April 2017, the most recent version was Release 6.

The future of MIPS has shifted recently. In December 2018, a company called Wave Computing tried to make the MIPS ISA open-source. This was called the MIPS Open initiative. It aimed to let people use the designs without paying licensing or royalty fees. However, this program was shut down later that year. In March 2021, Wave Computing announced that the development of the MIPS architecture had ended. The company decided to transition to a new architecture called RISC-V. Even though MIPS development has ceased, some companies like Loongson continue to use MIPS-compatible designs for their own special chips.

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