As we have just said, the machine instructions (code) provide the computer
with the means to carry out various operations; both internal and external. Internal
and external operations include processing the data and interfacing with other
computers, peripherals, and display and communications systems as part of a
computer system and performing maintenance.
The man/machine interfaces enable you to communicate with the computer’s
hardware and software through controlling devices and software/programs.
After completing this chapter, you should be able to:
Describe and recognize instruction types and their uses
Describe the types of instructions, their designator and classes, used by
computers
Describe how to interface with a computer’s hardware and software
We begin by discussing computer instructions; program types; and instruction
levels, types, interpretation, formats, sizes, and operand addressing.
TOPIC 1—COMPUTER
INSTRUCTIONS
Computer instructions tell the equipment to
perform a designated operation. These machine
instructions are contained in an instruction set (the
computer’s repertoire of instructions). They will be
processed by the CPU. Some computers have an I/O
controller (IOC) unit with its own set of instructions.
Each instruction in the set/repertoire contains at least an
operation (op) code to tell the CPU what operation to
perform. It may also contain an operand to identify the
address part of the instruction and/or other information
(designators) needed by the CPU to perform the
operation.
Before we discuss individual instruction types and
formats, let’s look at some of the types of computer
programs/software commonly used.
TYPES OF COMPUTER
PROGRAMS/SOFTWARE
A computer program is a sequence of instructions,
written in a specified way to perform a plan (an
algorithm) and/or routine. Programs are written to
manage a computer and its resources, solve a problem
or type of problem, and/or diagnose malfunctions in a
computer. Programs include hardwired (read-only)
programs stored in a read-only memory (ROM) or
programmable ROM (PROM). They also include
programs that were written by programmers and can
be altered (authorized software changes) as required.
Hardwired programs are installed at the factory and
cannot be altered except by replacing the ROM or
reprogramming the PROM. Other programs are
generally stored on magnetic media (tape or disk) or on
optical compact disk (CD) ROM. These programs are
loaded into computer memory when needed.
You will encounter several general types of
programs. These include operating systems,
application/operational programs, and utility programs
(utilities). Programs may be written to run on a
stand-alone computer or interactively on two or more
computers connected together.
Operating Systems
An operating system is a collection of many
programs used by a computer to manage its own
resources and operations. The types of operating
systems include the following:
Single tasking
Multitasking
Real-time
Local-area network
Wide-area network
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