BYU CS 345OS Overview (Chapter 1)1 CS 345 Stalling’s Chapter#Project 1: Computer System Overview...

BYU CS 345 OS Overview (Chapter 1) 1

CS 345

Stalling’s Chapter # Project

1: Computer System Overview2: Operating System Overview

4 P1: Shell

3: Process Description and Control4: Threads

4 P2: Tasking

5: Concurrency: ME and Synchronization6: Concurrency: Deadlock and Starvation

6 P3: Jurassic Park

7: Memory Management8: Virtual memory

6 P4: Virtual Memory

9: Uniprocessor Scheduling10: Multiprocessor and Real-Time Scheduling

6 P5: Scheduling

11: I/O Management and Disk Scheduling12: File Management

8 P6: FAT

Student Presentations 6

BYU CS 345 Project 1 - Shell 2

1. Compile and Validate

A task is a unit of execution (also referred to as a process). A shell (Command Language Interpreter) is a task that functions as an

interface between the user and an Operating System. A shell interprets textual commands coming either from the user’s

keyboard or from a script file and executes the commands either directly or creates a new child process to execute the command.

For Project 1: Download all the project files from class website.

os345.c, os345interrupts.c, os345signals.c os345tasks.c, os345semaphores.c os345.h, os345config.h, os345signals.h os345p1.c, os345p2.c, os345p3.c, os345p4.c, os345p5.c, os345p6.c os345park.c, os345park.h, os345lc3.c, os345lc3.h, os345mmu.c, os345fat.c,

os345fat.h Edit os345config.h (if necessary) to select host OS/IDE/ISA. (Only enable

one of the following defines: DOS, GCC, MAC, or NET.) Compile and execute your OS.


Why CS 345?


Operating Systems

What is an operating system? Hard to define precisely, because operating systems

arose historically as people needed to solve problems associated with using computers.

How about…“Software that makes computing power available to

users by controlling the hardware.”

“Software executes when nothing else is happening.”

“A collection of software modules including device drivers, libraries, and access routines.”


What Does a Modern OS Do?

Provides Abstractions: Hardware has low-level physical resources with

complicated, idiosyncratic interfaces. OS provides abstractions that present clean interfaces. Goal: make computer easier to use. Examples: Processes, Unbounded Memory, Files,

Synchronization and Communication Mechanisms. Provides Standard Interface:

Goal: portability. Unix runs on many very different computer systems.


What Does a Modern OS Do?

Mediates Resource Usage: Goal: allow multiple users to share resources fairly,

efficiently, safely and securely. Examples:

Multiple processes share one processor. (preemptable resource)

Multiple programs share one physical memory (preemptable resource).

Multiple users and files share one disk. (non-preemptable resource)

Multiple programs share a given amount of disk and network bandwidth (preemptable resource).

Consumes Resources: Solaris takes up about 8 Mbytes physical memory (or about

$400).


The Future…

In the future, computers will continue to become physically smaller and more portable.

Operating systems have to deal with issues like disconnected operation and mobility.

Media rich information within the grasp of common people - information with psuedo-real time components like voice and video.

Operating systems will have to adjust to deliver acceptable performance for these new forms of data.


Finally

Operating systems are so large no one person understands whole system. Outlives any of its original builders.

The major problem facing computer science today is how to build large, reliable software systems.

Operating systems are one of very few examples of existing large software systems, and by studying operating systems we may learn lessons applicable to the construction of larger systems.

Chapter 1 – Computer Systems

Let’s figure out what’s inside this thing...

OS Overview (Chapter 1) 10

Learning Objectives

Describe the basic elements of a computer system and their interrelationship.

Explain the steps taken by a processor to execute an instruction. Understand the concept of interrupts and how and why a processor

uses interrupts List and describe the levels of a typical computer memory

hierarchy. Explain the basic characteristics of multiprocessor and multicore

organization. Discuss the concept of locality and analyze the performance of a

multilevel memory hierarchy. Understand the operation of a stack and its use to support

procedure call and return.

BYU CS 345

OS Overview (Chapter 1) 12BYU CS 345

Computer Systems

Registers Interrupts Caching Input/Output Protection

Objectives

What is a computer system?

What are the basic elements of a computer system?


Computer Systems

Registers Interrupts Caching Input/Output Protection Summary

Objectives


CPURegisters


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


Lots of Registers…Registers


Computer Systems

Registers

Interrupts Caching Input/Output Protection Summary


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


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


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 NextInstruction

Fetch NextInstruction

ExecuteInstruction

ExecuteInstruction

Check forInterrupt:

Process Interrupt

Check forInterrupt:

Process Interrupt

Fetch Cycle Execute Cycle Interrupt Cycle

InterruptsDisabled

InterruptsEnabled

START

Interrupts


Multiple Interrupts

2 Choices Disable Interrupts

Disable upon entering an interrupt handler

Enable upon exiting Allow Interrupts

Allow an interrupt handler to be interrupted

Priorities?

Interrupts


Computer Systems

Registers Interrupts

Caching Input/Output Protection Summary


Memory Hierarchy

Registers

Cache

Main Memory

Disk Cache

Magnetic Disk

Magnetic Tape Optical Disk

More ExpensiveFaster & Smaller

BiggerSlower

Caching


Computer Systems

Registers Interrupts Caching

Input/Output Protection Summary


Programmed I/O

I/O module performs the action, not the processor

Sets appropriate bits in the I/O status register

No interrupts occur Processor is kept busy

checking status

Input / Output


Interrupt-Driven I/O

Processor is interrupted when I/O module ready to exchange data

Processor is free to do other work

No needless waiting Consumes a lot of processor

time because every word read or written passes through the processor

Input / Output


Direct Memory Access

Transfers a block of data directly to or from memory

An interrupt is sent when the task is complete

The processor is only involved at the beginning and end of the transfer

What does this mean with respect to a paged system?

Input / Output


Computer Systems

Registers Interrupts Caching Input/Output

Protection Summary


Hardware Protection

Why protect hardware? From what?

Shared hardware resources – memory, disk, … Errant programs

How? CPU provides 2 modes of operation

User Mode (non-privileged) Supervisor mode (privileged)

Privileged instructions can only be executed in monitor mode

All I/O instructions are privileged

Protection

Summary…


What is an O.S.?

Not always a clear definition as to what constitutes an O.S. and what is an application

CD-Rom Driver Scandisk Internet Explorer

Intermediary between the hardware and the users Allocate resources (CPU, Memory, disk space, etc.) between

programs and users efficiently Allow the user to conveniently access data and programs Protect the system from incorrect or malicious programs and

users

Summary


Hardware Review

Elements of a system:· Processor

Registers (address, data, control) Instruction cycle (fetch, decode, execute) Interrupts Usually includes hardware and special instructions to help

the O.S. manage memory, devices, etc.· Memory

Different levels (cache, main memory, disk) Operating system will generally manage memory (both

RAM and disk), and move data back and forth as required· I/O

Usually use Interrupts, DMA Operating system usually controls use of I/O devices

Summary


Registers

Used for frequently accessed items User-Visible registers – Available to the programmer and

compiler Data Registers Address Registers (Index, Segment, Stack Pointer) Condition code/flags

Control and Status registers – Used to control the processor

Program Counter/Instruction Pointer Memory address/data Processor Status Word Debugging registers Temp registers Memory Management registers

Summary


Interrupts

Interrupts Allow I/O devices to get the CPUs attention at regular

intervals (Program, Timer, I/O, Hardware failure) Helps the O.S. by reducing the time spent monitoring

I/O devices CPU checks for interrupts after each instruction, starts

the handler if needed May allow nested interrupts

I/O techniques Programmed I/O Interrupt-Driven I/O Direct Memory Access

Summary


Interrupts and I/O

Handling and Interrupts: Figure 1.10 (pg 23) Device sends interrupt request to CPU CPU finishes current instruction CPU acknowledges request CPU saves PC and PSW CPU loads PC with the address of the first instruction in the

interrupt handler (may get help from interrupt request) Interrupt handler starts, often saves other CPU registers and key

values Interrupt handler responds to the device Interrupt handler restores CPU registers and key values CPU restores PC and PSW and resumes previous program

Summary


Memory

Varying types of memory Registers, Cache, RAM, Disk, CD Vary in speed, size, cost CPU and O.S. try to keep frequently used data in faster memory

Cache – Use a small high-speed memory to improve the apparent speed of a larger low-speed memory

Keep track of what is currently being used, load into high-speed memory

Replacement Algorithm – What do we get rid of when we run out of memory?

Write Policy – How do we respond to modifications?

Summary


Topics to Cover…

OS Objectives OS Services Resource Manager Evolution Achievements

Processes Memory management Information protection and security Scheduling and resource management System architecture

BYU CS 345OS Overview (Chapter 1)1 CS 345 Stalling’s Chapter#Project 1: Computer System Overview...

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