Chapter 1. Computer System Overview

Chapter 1. Computer System Overview

Intruction Execution

A program to be execute by a processor consists of a set of instruction stored in memory. In its simplest form, instruction processing of two: the processor reads (fetches) intructions from memory one at a time and executes each instruction. Program execution consists of repeating the process of instruction fetch and instruction execution. The instruction execution may involve several opeartions and depend s on the nature of the instruction.

The processing requered for a single instruction is colled an instruction cycle. Using the simplified two-step description, the instruction cycle is depicted in Figure 1.2. the two steps are referred to as the fetch stage and the execute stage. Program execution halts only if the machine is turned off, some sort of unrecoverable error occurs, or a program instruction that halts the processor is encountered.


Figure 1.2. Basic Instructino Cycle

Instruction Computer

Instruction fetch: take instruction from program storage
Instruction decode: determining the required actions and instruction size
Operand fetch: get and put operand
Execute: Obtain and put operand
Result store: calculate the value of the outcome or status
Next instruction: determining the next instruction

The processor interprets the instruction and performs the required action. In general, these actions fall into your categories.

1. Processor memory : data may be transferred from processor to memory or from memory to processor.
2. Processor I/O : Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module.
3. Data processing : the processor may perform some arithmetic or logic operation on data.
4. Control : An instruction may specify that the sequence of execution be altered.

Source :
William Stallings, “Operating Systems “Internals and Design Principles”, Fifth Edition, Pearson Education Internationl
Related Post :
Basic Elements
Processor Register
Intruction Execution
Interupts
The Memory Hierarchycal
Cace Memory
I/O Communication
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