 Text book:
 Dinosaur book （恐龙书）

操作系统概念 ( 中译本 )
 Teacher:

郑扣根（ Zheng Kougen ）
 Prof. Dr. Mr.
…
 zhengkg@263.net.cn
 zkg@cs.zju.edu.cn
 TA lxhzju@cs.zju.edu.cn
“OS Homework”

 Refs:
 Kernighan and Pike, The UNIX Programming
Environment, Prentice-Hall, 1984.
 W.R. Stevens, Advanced Programming in the UNIX
Environment, Prentice-Hall, 1992
 W.R. Stevens, UNIX Network Programming I,
Prentice-Hall, 1997.
 W.R. Stevens, UNIX Network Programming II,
Prentice-Hall, 1998.
 www.kernel.org

 What is an Operating System?
 Mainframe Systems
 Desktop Systems
 Multiprocessor Systems
 Distributed Systems
 Clustered System
 Real -Time Systems
 Handheld Systems
 Feature Migration
 Computing Environments

An operating system ( 操作系统 )
 manages the computer resources, such as CPUs,
Memories, Hard disks, and acts as an intermediary between the computer hardware and the computer user,
 provides the system services to user programs,
 provides an environment for executing programs.

What Is an Operating System?
The components of a computer system

What Is an Operating System?
The components of a computer system



Hardware
– provides basic computing resources (CPU, memory, I/O devices).
Operating system
– controls and coordinates the use of the hardware among the various application programs for the various users.
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).
 Users (people, machines, other computers).

What Is an Operating System?
User view




PC users （ PC 用户）： The OS is designed to mostly for ease of use, with some attention paid to performance, and none paid to resource utilization.
Mainframe or minicomputer users ( 大型机和小型机用
户 ) ： The OS is designed to maximize resource utilization.
Workstation users （工作站用户）： The OS is designed to compromise between resource utilization and individual usability.
Handheld users （手持设备用户）： Mostly for individual usability, but performance per amount of batter life is important as well.

What Is an Operating System?
System view
 An operating system is a resource allocator （分配器）
 An operating system is a control program that manages the execution of user programs to prevent errors and improper use of the computer.


An operating system is to execute user programs and to make solving user problems easier.
What is part of the OS
 An OS is anything a vendor ships.
 An OS is the kernel （内核） part and all else are applications.

The matter of what constitutes an OS is becoming important (Microsoft case in 1998)

What Is an Operating System?
System goals
 OS goals
 Convenience : Make the computer convenient to use.
 Efficiency : Use the computer hardware in an efficient manner.
 Building an OS is a complex task
 Designing and implementation
 Revising and updating
 Hardware support.
 To find out What the OS is and what it does, let us trace the evolution (not revolution) of OS.

 No OS （无操作系统）
 Batched OS （批处理操作系统）
 Multiprogrammed OS （多道程序操作系统）
 Time-sharing OS （多时操作系统）

 Designer, Implementer, Operator, User
 Designer, Implementer / Operator, User
 Drawbacks:
 Scheduling time
 Setup time
 slow

 The OS
 was always resident in memory
 automatically transferred control from one job to another.
 Batching:
 Programmers submitted jobs in a job control languages (shell, awk, perl)
 Operators batched together jobs with similar needs and ran them through the computer as a group.
 Drawbacks:
 fast CPU and slow I/O devices.

 Multiprogrammed OS (vs. uniprogrammed OS)
 Keeping many jobs in memory (see the next slide)
 Switching to another job if the CPU is idle
 As long as at least one job needs to execute, the CPU is never idle.
 Multiprogrammed OS
 Job scheduling for selecting a job to load into memory
 CPU scheduling for selecting which job to run
 Memory management
 Protection.
 Drawback: not interactive



Memory sharing
 multiprogramming
Memory sharing + time sharing
 multiprogramming + interaction (or multi-tasking)
 The CPU is rapidly multiplexed among several jobs that are kept in memory. (I/O operation is terribly slow!)
 Time-sharing OS
 Memory management (virtual memory) and protection
 File system, disk management
 Process synchronization ( 同步 ) and communication
 Deadlock handling （死锁处理） .

 Personal computers
 computer system dedicated to a single user.
 I/O devices – keyboards, mice, display screens, small printers.
 Individuals have sole use of computer and do not need advanced CPU utilization of protection features.
 User convenience and responsiveness not maximizing
CPU and peripheral utilization
 Can adopt some of the technology developed for larger operating system.
 Not much of utilization
 Protection, and so on
 Many possible OSes: (Windows, MacOS, UNIX, Linux)

 Two types
 Tightly coupled systems （紧耦合系统）
 Parallel systems or multiprocessor systems
 Processors share memory and a clock; communication usually takes place through the shared memory.
 Loosed coupled systems （松耦合系统）
 Distributed systems and clustered systems
 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 parallel systems:
 Increased throughput
 Economy of scale
 Increased reliability

 graceful degradation (The ability to continue providing service proportional to the level of surviving hardware). fail-soft systems (systems designed for graceful degration)
Asymmetric multiprocessing
（非对称处理）
 Master processor schedules and allocated work to slave processors.
 Each processor is assigned a specific task;
 More common in extremely large systems

 Symmetric multiprocessing (SMP)
（对称处理）
 Each processor runs an identical copy of the operating system.
 Many processes can run at once without performance deterioration.
 Most modern operating systems support SMP
 SMP and ASMP may be the result of either hardware and software

 Advantages of distributed systems.
 Resources Sharing
 Computation speed up
– load sharing
 Reliability
 Communications
 Requires networking infrastructure.
 Local area networks (LAN) or Wide area networks
(WAN)
 May be either client-server or peer-to-peer systems.

 Clustering allows two or more systems to share storage.
 Provides high reliability.
 Asymmetric clustering : one server runs the application while other servers standby.
 Symmetric clustering : all N hosts are running the application.

 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.
 Well-defined fixed-time constraints.
 Real-Time systems may be either hard or soft real-time.

Hard real-time:
 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
 Limited utility in industrial control of robotics
 Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.



Personal Digital Assistants (PDAs) ( 个人数字助理 )
Cellular telephones （手机 ), Pocket PC,
…
 Issues:
 Limited memory
 Slow processors
 Small display screens.

 Traditional computing
 Web-Based Computing
 Embedded Computing