CS345 01 - OS Overview

CS345 01 - OS Overview - Chapter 1 Computer Systems Lets...

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Chapter 1 – Computer Systems Let’s figure out what’s inside this thing...
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BYU CS 345 OS Overview (Chapter 1) 2 Topics to Cover… OS Objectives OS Services Resource Manager Evolution Achievements Processes Memory management Information protection and security Scheduling and resource management System architecture
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BYU CS 345 OS Overview (Chapter 1) 3 Computer Systems Registers Interrupts Caching Input/Output Protection Summary Objectives
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BYU CS 345 OS Overview (Chapter 1) 4 CPU Registers
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BYU CS 345 OS Overview (Chapter 1) 5 Processor Registers User-visible registers May be referenced by machine language Available to all programs - application programs and system programs Data Registers – can be changed by user Address Registers – could be separate from data register Stack Registers – user / supervisor stacks Condition Codes – results of operations Control and status registers May or may not be visible Program Counter (PC) – address of next instruction Instruction Register (IR) – most recently fetched instruction MAR/MBR – memory reference registers Program Status Word (PSW) – condition codes, interrupts, mode Registers
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BYU CS 345 OS Overview (Chapter 1) 6 Instruction Execution Processor executes instructions in a program Instructions are fetched from memory on at a time START START HALT HALT Fetch Next Instruction Fetch Next Instruction Execute Instruction Execute Instruction Fetch Cycle Execute Cycle Registers
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BYU CS 345 OS Overview (Chapter 1) 7 Lots of Registers… Registers
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BYU CS 345 OS Overview (Chapter 1) 8 Computer Systems Registers Interrupts Caching Input/Output Protection Summary
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BYU CS 345 OS Overview (Chapter 1) 9 Interrupts The interrupt was the principle tool available to system programmers in developing multi- tasking systems! Improves processing efficiency by allowing the processor to execute other instructions while an I/O operation is in progress A suspension of a process caused by an event external to that process and performed in such a way that the process can be resumed Interrupts
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BYU CS 345 OS Overview (Chapter 1) 10 Processing of Interrupts Classes of Interrupts Program arithmetic overflow division by zero execute illegal instruction reference outside user’s memory space Timer I/O Hardware failure An interrupt handler determines nature of the interrupt and performs whatever actions are needed Control is transferred to this program Generally part of the operating system Interrupts
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BYU CS 345 OS Overview (Chapter 1) 11 Interrupt Cycle Processor checks for interrupts If no interrupts fetch the next instruction for the current program If an interrupt is pending, suspend execution of the current program, and execute the interrupt handler HALT Fetch Next Instruction Fetch Next Instruction Execute Instruction Execute Instruction Check for Interrupt:
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