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An addressing mode specifies how to calculate the effective memory address of an operand by using information held in registers and/or constants contained within a machine instruction or elsewhere. In computer programming, addressing modes are primarily of interest to those who write in assembly languages and to compiler writers.
The first was the CISC (Complex Instruction Set Computer), which had many different instructions. In the 1970s, however, places like IBM did research and found that many instructions in the set could be eliminated. The result was the RISC (Reduced Instruction Set Computer), an architecture that uses a smaller set of instructions.
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.
When computers were so costly that they were only or mainly used for science and engineering, word addressing was the obvious mode. As it became cost-effective to use computers for handling text, hardware designers moved to byte addressing. To illustrate why byte addressing is useful, consider the IBM 7094, which is word-addressable and has no ...
The design of the CPU allows RISC computers few simple addressing modes [2] and predictable instruction times that simplify design of the system as a whole. The conceptual developments of the RISC computer architecture began with the IBM 801 project in the late 1970s, but these were
In computer engineering, an orthogonal instruction set is an instruction set architecture where all instruction types can use all addressing modes.It is "orthogonal" in the sense that the instruction type and the addressing mode may vary independently.
This allows operating systems to use these segments for special purposes. Unlike the global descriptor table mechanism used by legacy modes, the base address of these segments is stored in a model-specific register. The x86-64 architecture further provides the special SWAPGS instruction, which allows swapping the kernel mode and user mode base ...
A complex instruction set computer (CISC / ˈ s ɪ s k /) is a computer architecture in which single instructions can execute several low-level operations (such as a load from memory, an arithmetic operation, and a memory store) or are capable of multi-step operations or addressing modes within single instructions.