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CS 345 Stalling’s Chapter # Project 1: Computer System Overview 2: Operating System Overview 4 P1: Shell 3: Process Description and Control 4: Threads 4 P2: Tasking 5: Concurrency: ME and Synchronization 6: Concurrency: Deadlock and Starvation 6 P3: Jurassic Park 7: Memory Management 8: Virtual memory 6 P4: Virtual Memory 9: Uniprocessor Scheduling 10: Multiprocessor and Real-Time Scheduling 6 P5: Scheduling 11: I/O Management and Disk Scheduling 12: File Management 8 P6: FAT Student Presentations 6 BYU CS 345 OS Overview (Chapter 1) 1 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. BYU CS 345 Project 1 - Shell 2 Why CS 345? BYU CS 345 OS Overview (Chapter 1) 3 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.” BYU CS 345 OS Overview (Chapter 1) 4 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. BYU CS 345 OS Overview (Chapter 1) 5 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). BYU CS 345 OS Overview (Chapter 1) 6 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. BYU CS 345 OS Overview (Chapter 1) 7 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. BYU CS 345 OS Overview (Chapter 1) 8 Chapter 1 – Computer Systems Let’s figure out what’s inside this thing... 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) 10 Objectives Computer Systems What is a computer system? What are the basic elements of a computer system? Registers Interrupts Caching Input/Output Protection BYU CS 345 OS Overview (Chapter 1) 12 Objectives Computer Systems Registers Interrupts Caching Input/Output Protection Summary BYU CS 345 OS Overview (Chapter 1) 13 Registers CPU BYU CS 345 OS Overview (Chapter 1) 14 Registers 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 BYU CS 345 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 OS Overview (Chapter 1) 15 Registers Lots of Registers… BYU CS 345 OS Overview (Chapter 1) 17 Computer Systems Registers Interrupts Caching Input/Output Protection Summary BYU CS 345 OS Overview (Chapter 1) 18 Interrupts Interrupts The interrupt was the principle tool available to system programmers in developing multitasking 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 BYU CS 345 OS Overview (Chapter 1) 19 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 BYU CS 345 OS Overview (Chapter 1) 20 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 Fetch Cycle Execute Cycle Interrupt Cycle Interrupts Disabled START Fetch Next Instruction Execute Instruction Interrupts Enabled Check for Interrupt: Process Interrupt HALT BYU CS 345 OS Overview (Chapter 1) 21 Interrupts Multiple Interrupts 2 Choices Disable Interrupts Disable upon entering an interrupt handler Enable upon exiting Allow Interrupts BYU CS 345 Allow an interrupt handler to be interrupted Priorities? OS Overview (Chapter 1) 23 Computer Systems Registers Interrupts Caching Input/Output Protection Summary BYU CS 345 OS Overview (Chapter 1) 26 Caching Memory Hierarchy More Expensive Faster & Smaller Registers Cache Main Memory Disk Cache Magnetic Disk Magnetic Tape BYU CS 345 Bigger Slower Optical Disk OS Overview (Chapter 1) 27 Computer Systems Registers Interrupts Caching Input/Output Protection Summary BYU CS 345 OS Overview (Chapter 1) 31 Input / Output 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 BYU CS 345 OS Overview (Chapter 1) 32 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 BYU CS 345 OS Overview (Chapter 1) 33 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? BYU CS 345 OS Overview (Chapter 1) 34 Computer Systems Registers Interrupts Caching Input/Output Protection Summary BYU CS 345 OS Overview (Chapter 1) 35 Protection 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 BYU CS 345 OS Overview (Chapter 1) 36 Summary… 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 BYU CS 345 OS Overview (Chapter 1) 41 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 BYU CS 345 OS Overview (Chapter 1) 42 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 BYU CS 345 OS Overview (Chapter 1) 43 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 BYU CS 345 OS Overview (Chapter 1) 44 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 BYU CS 345 OS Overview (Chapter 1) 45 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? BYU CS 345 OS Overview (Chapter 1) 46 BYU CS 345 OS Overview (Chapter 1) 47 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 345 OS Overview (Chapter 1) 48