TOPIC 1—COMPUTER INSTRUCTIONS

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 8-2