An instruction cycle' (also called fetch-and-execute cycle,
fetch-decode-execute cycle, and FDX) is the time period during which a computer
processes a machine language instruction from its memory or the sequence of
actions that the central processing unit (CPU) performs to execute each machine
code instruction in a program.
The name fetch-and-execute cycle is commonly used. The instruction must be
main memory, and then executed by the CPU. This is fundamentally how
a computer operates, with its CPU reading and executing a series of instructions
written in its machine language. From this arise all functions of a computer
familiar from the user's end.
How does a computer process instructions?
The term instruction cycle refers to the process in which a
computer executes a single instruction. The instruction
cycle is repeated each time the computer excites an
instruction. The steps in the cycle are summarized in the
Few people nowadays remember that the IBM PC was
not the first "personal computer" and that MS-DOS was not the first industry
standard operating system. In fact, MS-DOS was but an imperfect copy of the
operating system that really has a claim to that title.
The first generation of personal computers (or microcomputers, as they were
known then) used chips like the Intel 8008, 8080, Zilog Z80, MOS Technology 6502
and Motorola 6800. While some early microcomputers (for example, the Apple II)
used proprietary operating systems, hundreds of different manufacturers licensed
a product called CP/M (as in Control Program / Monitor) made by a company
called Digital Research. Long before the IBM PC and its clones / compatibles,
the CP/M architecture provided for industry standard software that was portable
across hundreds of different brands and models. This was DRI founder Gary
Kildall's main contribution to the software industry. Microsoft simply followed
in DRI's footsteps.