Operating Systems

1. Operating Systems Chapter 1 Introduction Text book: Applied Operating System Concepts by Silberschatz, Galvin, and Gagne

2. Module 1: Introduction • What is an operating system? • Simple Batch Systems • Multiprogramming Batched Systems • Time-Sharing Systems • Personal-Computer Systems • Parallel Systems • Distributed Systems • Real -Time Systems

3. What is an Operating System? § 1.1 • A program that acts as an intermediary between a user of a computer and the computer hardware. • Purpose: provide an environment in which a user can execute programs. • Primary goals: • Execute user programs and make solving user problems easier. • Make the computer system convenient to use. • Secondary goal: • Use the computer hardware in an efficient manner.

4. Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users – trying to solve different problems (people, machines, other computers).

5. Abstract View of System Components

6. Operating System Definitions 資源配置 • Resource allocator– manages and allocates resources. (CPU time, memory space, file-storage space, I/O devices…) Since there maybe many – possibly conflicting – requests for resources, the OS must decide which requests are allocated resources so that it can operate the computer system efficiently and fairly.

7. Operating System Definitions • Control program– controls the execution of user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices . • Kernel – the one program running at all times (all else being application programs). 核心程式

8. Computer Architecture can help • The primary goal of OS – convenient for the user – and the second goal – efficient – are sometimes contradictory. • Operating systems and computer architecture have had a great deal of influence on each other. • As OS were designed and used, it become obvious that changes in the design of the hardware could simplify them. 計算機結構

9. Simple Batch Systems § 1.2 控制台 • Early computers were (physically) enormously large machines run from a console. The common input devices were card readers and tape drives. • The major task of OS was to transfer control automatically from one job to the next. • The OS was always resident in memory. • To speed up processing, operators batched together jobs with similar needs and ran them through the computer as a group.

10. Memory Layout for a Simple Batch System

11. Improving batch system 閒置 • In batch system, the CPU is often idle, because the speeds of the mechanical I/O devices are intrinsically slower than are those of electronic devices. • Disk technology allowed the OS to keep all jobs on a disk and access them directly. It could do job scheduling to use resources and perform tasks efficiently. • The most important aspect of job scheduling is the ability to multiprogram. 本質上 工作排程

12. Multiprogrammed Batch Systems 多程式批次系統 Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. 多路傳輸，多工 Multiprogramming increases CPU utilization by organizing jobs such that the CPU always has one to execute.

13. OS Features Needed for Multiprogramming • Job Scheduling – If several jobs are ready to be brought into memory, and if there is not enough room for all of them, the the system must choose among them. • Memory management – the system must allocate the memory to several jobs. • CPU scheduling – the system must choose among several jobs ready to run at the same time.

14. Time-Sharing Systems § 1.3 分時系統 多工 • Time sharing, or multitasking, is a logical extension of multiprogramming. • An interactive, or hands-on, computer system provides direct communication between the user and the system. • A time-shared OS allows the many users to share the computer simultaneously. As the system switches rapidly from one user to the next, each user is given the impression that the entire computer system is dedicated to her use. 奉獻，專用

15. Time-Sharing Systems • A program that is loaded into memory and is executing is commonly referred to as a process. • When a process executes, it typically executes for only a short time before it either finishes or needs to perform I/O. • Rather than let the CPU sit idle when I/O takes place, the OS will rapidly switch the CPU to the program of some other user. • Although some batch processing is still done, most systems today are time sharing. 程序

16. Personal-Computer Systems § 1.4 • Personal computers– computer system dedicated to a single user. Example OS: Microsoft Windows, Apple Macintosh, OS/2, Linux. • Features that were at one time available on only main frames have been adopted by microcomputers. Example: MULTICS. • Personal workstation is a large PC – for example, the Sun SPARCstation, the HP/Appolo, the IBM RS/6000, or the Intel Pentium system running Windows NT or a UNIX derivatives.

17. Migration of Operating-System Concepts and Features

18. Parallel Systems § 1.5 • Multiprocessor systems with more than one CPU in close communication. • Tightly coupled system– processors sharing the computer bus, the clock, and sometimes memory and peripheral devices. • Advantages of parallel system: • Increased throughput • Economical: can share peripherals, mass storage, and power supplies. • Increased reliability • graceful degradation • Fault tolerant. 緊密耦合 匯流排

19. Symmetric Multiprocessing (SMP) • Each processor runs an identical copy of the operating system, and these copies communicate with one another as needed. • Many processes can run at once without performance deterioration. • Most modern operating systems support SMP

20. Asymmetric Multiprocessing 非對稱 • Each processor is assigned a specific task; master processor schedules and allocates work to slave processors. • This scheme defines a master-slave relationship. • More common in extremely large systems

21. Off-load to back-ends As microprocessors become less expensive and more powerful, additional OS functions are off-loaded to slave processors, or back-ends. For example: add a microprocessor with its own memory to manage a disk system. This use of microprocessors has become so common that it is no longer considered multiprocessing.

22. Real-Time Systems § 1.6 • Used when there are rigid time requirements on the operation of a processor or the flow of data. • Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. • Processing must be done within the defined constraints, or the system will fail. • A real-time system is considered to function corretly only if it returns the correct result within any time constraints. • Well-defined fixed-time constraints.

23. Real-Time Systems § 1.6 即時系統 • Hard real-time system. • Secondary storage limited or absent, data stored in short-term memory, or read-only memory (ROM) • Conflicts with time-sharing systems, not supported by general-purpose operating systems. • Soft real-time system • A critical real-time task gets priority over other tasks. • Limited utility in industrial control or robotics • Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

24. Distributed Systems 分散式系統 • Distribute the computation among several physical processors. • Loosely coupled system– each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines. • Advantages of distributed systems. • Resources Sharing • Computation speed up – load sharing • Reliability • Communications

25. Distributed Systems • Network Operating System • provides file sharing • provides communication scheme • runs independently from other computers on the network • Distributed Operating System • less autonomy between computers • gives the impression there is a single operating system controlling the network. 網路作業系統 分散式作業系統