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An orthogonal instruction set does not impose a limitation that requires a certain instruction to use a specific register [1] so there is little overlapping of instruction functionality. [ 2 ] Orthogonality was considered a major goal for processor designers in the 1970s, and the VAX-11 is often used as the benchmark for this concept.
An instruction set architecture (ISA) is an abstract model of a computer, also referred to as computer architecture.A realization of an ISA is called an implementation.An ISA permits multiple implementations that may vary in performance, physical size, and monetary cost (among other things); because the ISA serves as the interface between software and hardware.
An instruction set architecture is distinguished from a microarchitecture, which is the set of processor design techniques used, in a particular processor, to implement the instruction set. Processors with different microarchitectures can share a common instruction set.
This allowed the 360's ISA to be expansive, and this became the paragon of computer design in the 1960s and 70s, the so-called orthogonal design. This style of memory access with wide variety of modes led to instruction sets with hundreds of different instructions, a style known today as CISC (Complex Instruction Set Computing).
The term is most-frequently used regarding assembly instruction sets, as orthogonal instruction set. Orthogonality in a programming language means that a relatively small set of primitive constructs can be combined in a relatively small number of ways to build the control and data structures of the language. [2]
The VAX is well known for its highly "orthogonal" instruction set architecture (ISA), in which any instruction can be applied to any data. For instance, an ADD instruction might add the contents of two processor registers , or one register against a value in memory, two values in memory, or use the register as an offset against an address.
The x86 instruction set refers to the set of instructions that x86-compatible microprocessors support. The instructions are usually part of an executable program, often stored as a computer file and executed on the processor. The x86 instruction set has been extended several times, introducing wider registers and datatypes as well as new ...
This made the CISCs easier to program, because a programmer could remember only thirty to a hundred instructions, and a set of three to ten addressing modes rather than thousands of distinct instructions. This was called an orthogonal instruction set. The PDP-11 and Motorola 68000 architecture are examples of nearly orthogonal instruction sets.