What’s an Instruction Set?

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An instruction set, or instruction set architecture, is the collective set of commands that a computer processor can execute. Everything a computer does, from running a word processing application to encoding video files, is reducible to a combination of these commands. Programmers don’t create programs directly using these instructions, but instead use a special type of software known as a compiler that translates programming code into machine instructions. Most personal computers use an instruction set first used in the 1970s, while smartphones, tablets, and other devices use simpler instruction sets optimized for low-power environments.

Computers may appear to be capable of unlimited tasks, but the microprocessors within them are capable of executing only a limited number of predefined commands, known as instructions. By itself, each instruction is relatively simple, perhaps telling the processor to add two numbers or move a data from one location to another. When combined, these basic instructions become quite powerful and are used as the foundation for all kinds of software. The performance and compatibility of a CPU is directly related to the number and type of instructions supported by the CPU, making the instruction set critical to the commercial success or failure of any new design.

A CPU can only execute functions that are part of its instruction set, but very few computer programmers incorporate these commands into their software. Instead, an intermediate step known as compilation is used. In this process, a program known as a compiler translates the easy-to-use code used by programmers into “machine code” that the processor understands. Because different computer processors support different instruction sets, a compiler must be designed for the type of processor on which the program is intended to run. With modern microprocessors capable of executing as many as hundreds of millions or even billions of instructions in just one second, compilers have become the only practical means of creating computer software.

The microprocessors used in nearly every personal computer sold since the 1980s use an instruction set called x86, originally designed for an Intel® processor that debuted in the mid-1970s. The desire for backward compatibility has helped keep x86 dominant in the PC market, even as new instructions are occasionally added via extensions. Many smartphones, tablets, and other types of consumer electronics use microprocessors based on the ARM instruction set, which is simpler and more energy efficient than x86. High-end servers, super computers, and other specialized devices such as game consoles can use different instruction sets.

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