Symbols, Instructions and Microcode

SYMBOLS

A symbol is a value that is represented by a serise of binary ones and zeroes. Symbols are the simplest representation of the relationship between computer binary values and the information that the binary values represent. An example of a human readable symbol are the letters and numbers we humans recognize. Another form is the mnemonic symbols used by humans to represent instructions in assembly language. A third type of symbol is the symbol set used by quadrature amplitude modulation where 128 analog signal values are used to represent various combinations of seven binary zeroes and ones.

Instructions

Instructions are basic commands composed of one or more symbols that when passed to a processor as input, produce a specific output pattern. Functions an instruction can perform include adding two numbers, subtracting two numbers, reading a byte from input, write a byte etc. Processors differ in their physical architecture and in their instruction set.

Microcode

Microcode is a logically organized set of instructions that allows the computer to perform a basic task such as writing information to the monitor or reading a keystroke from the keyboard. The microcode is built into the processor. By stringing together multiple sets of microcode instructions, programs can accomplish complex tasks. This microcode is usually not accessible to the programs running on the processor that stores the microcode, but they can request that certain microcode be run.