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CSS430 Introduction Textbook Ch1 – Ch2 These slides were compiled from the OSC textbook slides (Silberschatz, Galvin, and Gagne) and the instructor’s class materials. CSS430 Introduction 1 Course Objectives You will: Study the fundamental concepts of operating systems Practice the logical design using Java But not: Learn how to use/hack Windows and Linux If this is your main objective, you should take R140/145/R708 of UW Computing Training http://www.washington.edu/computing/training Skill up system programming with C++ Program 1 will deal with several system calls, but if this is your main interest, you should take CSS432, CSS434 or other C++ programming courses. CSS430 Introduction 2 Other Noteworthy OSes Distributed OSes All blends of *NIX Any windows competitor IBM PS/2 NeXT OS Commodore 64 Embedded OSes Low-power OSes CSS430 Introduction 3 Important Time Lines Program 1: System calls and shell Program 2: Scheduler Midterm: Process Management Program 3: Synchronization Program 4: Paging Final: Memory/File Management Project: Unix-like file system (Check the syllabus for their due dates.) CSS430 Introduction 4 Important Web Pages and Email Addresses Our class web: http://courses.washington.edu/css430/index.html Java: http://java.sun.com/j2se/1.4/docs/api/index.html Instructor’s email: {mfukuda, ksung, or rynn}@u.washington.edu Class discussion mailing list: Use the message board. Assignment submission: Use Catalyst drop box. CSS430 Introduction 5 What is an Operating System Goals Making the computer system convenient to use Using computer hardware in an efficient manner Definitions Resource allocator – manages and allocates resources Control program – controls the execution of user programs and operations of I/O devices Kernel – the one program running at all times (all else being application programs) CSS430 Introduction 6 Computer System Components CSS430 Introduction 7 OS - Intermediary The OS acts on our behalf as a micromanager An OS acts as an intermediary between the computer and the user It should use resources fairly and efficiently; ease of use It should protect users from one another, and from the kernel CSS430 Introduction 8 From the Text “an OS is similar to a government” CSS430 Introduction 9 More from the Dino Book “Like a government, the OS performs no useful function by itself” CSS430 Introduction 10 O.S. & Computer Architecture As hardware is introduced, Oses are built to make the hardware useable As Oses evolve, it becomes obvious that certain hardware elements could simplify the operation of the kernel So, a back-and-forth cycle exists. CSS430 Introduction 11 Operating Systems History Batch systems: Multiprogramming: IBM360 Time-sharing systems: Multics, Unix Personal-computer systems: Windows, Linux Distributed systems: Amoeba, Mach CSS430 Introduction 12 Batch Systems A job is assembled of the program, the data, and some control information (in control cards). Programmers pass their jobs to an operator. The operator batched together jobs. OS transfers control from one job to another. Each job output is sent back to the programmer. CSS430 Introduction 13 Multiprogramming Several jobs are kept in main memory at the same time. OS picks one of them to execute. The job may have to wait for a slow I/O operation to complete. OS switches to and executes another job. To facilitate multiprogramming, OS needs: Job scheduling Memory management CSS430 Introduction 14 Time-Sharing Systems This is a logical extension of multiprogramming. Each user has at least one separate program in memory. A program in execution is referred to as a process. Process switch occur so frequently that the users can interact with each program while it is running. File system allows users to access data and program interactively. CSS430 Introduction 15 Personal-Computer Systems Personal computers – computer system dedicated to a single user. User convenience and responsiveness Can adopt technology developed for larger operating systems’ some features. At its beginning, a single user system didn’t not need advanced CPU utilization and protection. Later, file protection is necessary to avoid virus. Overall, the same OS concepts are appropriate for the various different classes of computers. CSS430 Introduction 16 Parallel Systems Multiprocessor systems with more than one CPU in close communication (in one box). Tightly coupled system – processors share memory and a clock; shared-memory-based communication. Advantages of parallel system: Increased throughput Economical Increased reliability CSS430 Introduction 17 Distributed Systems Loosely coupled system – each processor has its own local memory; message-based communication through various communications lines, such as SAN, LAN, WAN or telephone lines. Advantages of distributed systems. Resources Sharing (Printer, DB, special devices) Performance (load sharing, process migration) Reliability Communications http://directory.google.com/Top/Computers/Software/ Operating_Systems/Network/Distributed/ CSS430 Introduction 18 Real-Time Systems Dedicated to a single application: controlling scientific experiments, medical imaging systems, industrial, and military control systems (ex. Dam control, nuclear reactor, missile guiding, etc.). Hard deadline Hard real-time system. Data stored in short-term memory or ROM Conflicts with time-sharing systems Soft real-time system Best effort to meet the deadline Useful in applications (multimedia, virtual reality, QoS) CSS430 Introduction 19 Computer Hardware CSS430 Introduction 20 Synchronous I/O requesting process waiting user device driver kernel Interrupt handler Hardware data transfer During execution, each program needs I/O operations to receive keyboard inputs, open files, and print out results. At the early computer era, a program had to wait for an I/O operation to be completed. (Synchronous I/O) This frequently causes CPU idle. time CSS430 Introduction 21 Async I/O and Interrupts requesting process continuing user device driver kernel Interrupt handler Hardware data transfer time Asynchronous I/O returns control to a user program without waiting for the I/O to complete. When the I/O is completed, an interrupt occurs to CPU that temporarily suspends the user program and handles the I/O device. CSS430 Introduction 22 Discussions 1 1. What tasks should OS perform in order to suspend and resume a program? List them. Program suspension Program resumption 1. 2. .. 1. 2. .. CSS430 Introduction 23 Hardware Protection Purpose: With resource sharing, many programs could be affected by a bug in one program. Incorrect or malicious resource accesses cause a hardware trap to the operating system. Dual-Mode Operation: User mode: no privileged instructions allowed. Kernel mode: Privileged instructions allowed. I/O Protection: all privileged Memory Protection: A region from the base to the limit register allowed to use CPU Protection: CPU allowed to use until the timer gets 0. CSS430 Introduction 24 Dual-Mode Operations Provide hardware support to differentiate between at least two modes of operations. 1. User mode – execution done on behalf of a user. 2. Monitor mode (also supervisor mode, system mode, or Kernel mode) – execution done on behalf of operating system. Switching between two modes Device interrupts, hardware traps, system calls cause a trap to the kernel mode The operating system returns to the user mode after servicing requests. CSS430 Introduction 25 System Calls CSS430 Introduction 26 Discussions 2 Early computers did not have interrupts, timers, and/or privileged instructions. What features was OS unable to facilitate? Features not supported by HW Features not facilitated by OS Asynchronous I/O and interrupts Timers Privileged instructions CSS430 Introduction 27 Discussions 3 List three distinct events upon which OS can get back CPU from the current user program. 1. 2. 3. CSS430 Introduction 28 Project 1 – System Calls & Shells This warmup exercise has two parts: A C/C++ app that makes direct system calls to UNIX A Shell.java program that runs with ThreadOS CSS430 Introduction 29 Part 1 Experiment with User-to-OS APIs System calls in C/C++ on Unix See the list of system calls you are to use in the assignment CSS430 Introduction 30 Part 2 To get started, download the ThreadOS files at /usr/apps/css430/ThreadOS/ Grab the class files, too! You’ll need these more than the src for hw1 CSS430 Introduction 31 Grading Guide See http://courses.washington.edu/css430/ prog/prog1.html More on this Thursday CSS430 Introduction 32