Chapter 1
Operating System Overview
Contents
Operating System Objectives and Functions
The Evolution of Operating System
Major Achievements
Characteristics of Modern OS
Examples（NT、UNIX）
OPERATING SYSTEM OVERVIEW
1.1 Objectives and Functions (p45)
1.1.1 Overview
1.1.2 The Operating System as a User/Computer Interface
1.1.3 The Operating System as Resource Manager
1.1.4 Ease of Evolution of an Operating System
OPERATING SYSTEM OVERVIEW
1.1.1 Overview
An operating system is a program that manages the
computer, controls the execution of application
programs and acts as an interface(接口) between the
user of a computer and the computer hardware.
Objectives
‫ ٭‬Convenience（方便）
‫ ٭‬Efficiency（有效）
‫ ٭‬Ability to evolve（易扩展）
OPERATING SYSTEM OVERVIEW
1.1.2 OS as a User/Computer Interface (I)
End User
Programmers
Operating
System
Designer
Applications Programs
Utilities (Compiler, Database…)
Operating System
Computer Hardware
Figure 2.1 Layers and Views of a Computer System
OPERATING SYSTEM OVERVIEW
OS as a User/Computer Interface (II)
The operating system masks（隐藏） the details of
the hardware from the programmer，and provides
the programmer with a convenient interface for
using the system.
The types of system interface
‫ ٭‬Command interface: system command (internal、
external)
‫ ٭‬Graphics interface: windows
‫ ٭‬Programmer interface: system call, c-lib
OPERATING SYSTEM OVERVIEW
Services of the Operating System (I)
Program creation
‫ ٭‬Such as: fork (unix)、CreateProcess (win)
Program execution
‫ ٭‬Such as: execl, execp
Access to I/O devices
‫ ٭‬Such as: read/write
Controlled access to files
‫ ٭‬Such as: read/write
OPERATING SYSTEM OVERVIEW
Services of the Operating System (II)
System access
‫ ٭‬Provide protection and authorized
Error detection and response
‫ ٭‬Such as: error
Accounting
OPERATING SYSTEM OVERVIEW
1.1.3 OS as Resource Manager (I)（p47）
Types of Resource: CPU、Memory、Devices
CPU: chapter 3.4.5.6.9.10
Memory: chapter 7.8
I/O Devices: chapter 11.12
OPERATING SYSTEM OVERVIEW
OS as Resource Manager (II)
As a control mechanism is unusual in two respects
‫ ٭‬The OS functions in the same way as ordinary
computer software; that is, it is a program
executed by the processor.
‫ ٭‬The OS frequently relinquishes control (释放控
制)and must depend on the processor to allow it
to regain control（获取控制）.
OPERATING SYSTEM OVERVIEW
OS as Resource Manager (III Figure 2.2)
Management of CPU
Management of I/O Device
Management of Memory
Management of Files
Concept:
‫ ٭‬Kernel、Nucleus(内核): Always in main
memory, contains the most-frequently-used
functions
OPERATING SYSTEM OVERVIEW
1.1.4 Ease of Evolution（p49）
Reasons for evolution
‫ ٭‬hardware upgrades
▪ Exp: support paging
‫ ٭‬new services
‫ ٭‬fixes
Implements
‫ ٭‬software engineering: modules、layer、
object design
OPERATING SYSTEM OVERVIEW
1.2 The Evolution of Operating Systems
1.2.1 Serial Processing
1.2.2 Simple Batch Systems
1.2.3 Multiprogrammed（多道） Batch Systems
1.2.4 Time-Sharing Systems
OPERATING SYSTEM OVERVIEW
1.2.1 Serial Processing(p50串行处理)
Example
‫ ٭‬Input  Calculate  Print
Problems
‫ ٭‬Scheduling: The estimated time is not accurate
‫ ٭‬Setup time: Between the setup procedure, if an
error occurred, then must go back to the
beginning of the setup sequence
‫ ٭‬Contradiction between human and machine
OPERATING SYSTEM OVERVIEW
1.2.2 Simple Batch System
Objectives：Solution contradiction between human
and machine
‫ ٭‬User submits the job on cards or tape to a
computer operator (use JCL（job control
language))
Implement: Monitor
OPERATING SYSTEM OVERVIEW
From the Point of View of the Monitor (p51)
Interrupt
processing
Device
Drivers
Job
Sequencing
Control Language
Interpreter
 Monitor is responsible for the
running of every job
monitor
 Controls are transferred between
monitor and other user programs
User Program
Area
Memory layout for a resident(驻留) monitor
OPERATING SYSTEM OVERVIEW
From the Point of View of the Processor
When CPU runs command of monitor, the monitor
gains the control.
When CPU runs command of user program, the
user program gains the control.
Transfer the control: First monitor gains the control,
when user program load in, it gains the control,
when the user program finish or error, the monitor
regains（重获） the control.
OPERATING SYSTEM OVERVIEW
JCL (Job Control Language)
$JOB
$FTN
…Fortran
$LOAD
$RUN
$END
//begin
//using Fortran compile and link
//instructions
//load in runable modules
//running.
//finish do the job
OPERATING SYSTEM OVERVIEW
Other Hardware Feature Desirable(p53)
 Memory protection（内存保护）: User space and system
space are independent.
‫ ٭‬E.g. Hardware can detect outside accessing error.
 Timer interrupt（时钟中断）: When the timer expires, an
interrupt occurs.
 Privileged instructions（特权指令）: Can be executed only
by the monitor.
 Interrupts:
‫ ٭‬Improvement efficiency
‫ ٭‬Easy for relinquishing（释放） and regaining control
OPERATING SYSTEM OVERVIEW
1.2.3 Multiprogrammed Batch Systems
 Uniprogramming（单道） has low efficiency（效率）:
‫ ٭‬CPU---I/O contradiction
Read one record
Execute 100 instructions
Write one record
TOTAL
0.0015 seconds
0.0001 seconds
0.0015 seconds
0.0031 seconds
Percent CPU Utilization = 0.0001/0.0031=3.2%
Figure 2.4 System Utilization Example
OPERATING SYSTEM OVERVIEW
Multiprogramming/Multitasking
There are many user programs in the
memory.
Hardware need for Multiprogramming.
‫ ٭‬Interruption
For example: p55 Fig2.5
OPERATING SYSTEM OVERVIEW
Example of Multiprogramming
 256k available memory
 Notes: not consider the resource competition
Type of JOB
JOB1
Heavy Computer
JOB2
Heavy I/O
JOB3
Heavy I/O
Duration
5min
15min
10min
Memory required
50k
100k
80k
Need disk
No
No
Yes
Need terminal
No
Yes
No
Need printer
No
No
Yes
Table 2.1 Sample Program Execution Attributes
OPERATING SYSTEM OVERVIEW
Analysis
OPERATING SYSTEM OVERVIEW
Analysis
 Single
‫ ٭‬Processor use＝5/(5+15+10)=17%
‫ ٭‬Memory use=[(50*5+100*15+80*10)/256/30] =33%
‫ ٭‬Disk use=10/30=33%
‫ ٭‬Printer use＝10/30=33%
‫ ٭‬Total time＝ 5+15+10＝30
‫ ٭‬Throughput ＝6 job/hour
‫ ٭‬Mean response time＝（5+20+30）/3=18
OPERATING SYSTEM OVERVIEW
Analysis
 Multiprogramming
‫ ٭‬Processor use＝5/15=33%
‫ ٭‬Memory use=[(50+100+80)*5+(100+80)*5+100*5]/256/15
=65%
‫ ٭‬Disk use=10/15=67%
‫ ٭‬Printer use＝10/15=67%
‫ ٭‬Total time＝15
‫ ٭‬Throughout ＝12job/hour
‫ ٭‬Mean response time＝（5+10+15）/3=10
OPERATING SYSTEM OVERVIEW
Sophisticated(复杂性) of Multiprogramming (p57)
Memory management
Scheduling
‫ ٭‬Algorithm（算法）: The processor（处理器）
must decide which one to run.
OPERATING SYSTEM OVERVIEW
1.2.4 Time-Sharing Systems
 Multiple users simultaneously（同时） access the system
through terminals(终端)
 Concepts:
‫ ٭‬time slice（时间片）: q
‫ ٭‬user num（用户数）: n
‫ ٭‬response time（响应时间）: t
‫ ٭‬t=n×q
 Mode: multi-terminals、multi-windows
OPERATING SYSTEM OVERVIEW
Batch Multiprogramming vs Timer Sharing
Batch
Multiprogramming
Principal
objective
Source of
instruction to
operating system
Time Sharing
Maximize processor
use
Minimize response
time
Job control language
commands provided
with the job
Commands entered
at the terminal
OPERATING SYSTEM OVERVIEW
Reducing the Swapping Loads by Partial Swapping（p59）
Reducing the spending for accessing disk
OPERATING SYSTEM OVERVIEW
1.3 Major Achievements（p60）
1.3.1 Processes(进程)
1.3.2 Memory management
1.3.3 Information protection and security
1.3.4 Scheduling and resource management
1.3.5 System structure
OPERATING SYSTEM OVERVIEW
1.3.1 Processes
 A program in execution
 The animated spirit（活动精灵） of a program
 The entity（实体） that can be assigned（分派） to and
executed on a processor
 Three major types of computer system
‫ ٭‬Multiprogramming batch operation
‫ ٭‬Time sharing
‫ ٭‬Real-time transaction（处理） systems
OPERATING SYSTEM OVERVIEW
Errors May Happen in Multiprogramming
Improper synchronization（同步）: Signals being
lost or duplicate（重复） signals being received.
Failed mutual exclusion(失败的互斥)
Nondeterminate（不确定） program operation:
The result is not unique
Deadlocks（死锁）
To solute these problems, introduce process concept
OPERATING SYSTEM OVERVIEW
Process entity(实体)
An executable program
The associated data needed by the program
The execution context(上下文) of the program
OPERATING SYSTEM OVERVIEW
Process Image and Process Switch（切换）(p63)
OPERATING SYSTEM OVERVIEW
1.3.2 Memory Management
Process isolation（隔离）
Automatic allocation and management
Support of modular（模块化） programming
Virtually memory
Long-term storage
Protection and access control（访问控制）
OPERATING SYSTEM OVERVIEW
Virtual
Processor
Read, Write
Virtual
Memory
Copy
(a) User’s View
Real
Processor
Virtual
Address
Files
Long-term Store
Mapper
(Address
Translate)
Memory
Address
Main
Memory
Swapping
Auxiliary
Memory
(b) Operating System Designer’s View
Fig 2.10 Two Views of a Storage System
OPERATING SYSTEM OVERVIEW
1.3.3 Information Protection and Security
Access control: for various resources in the system
Information flow control（信息流控）: to
guarantee the data to send to destination
Certification（认证）
OPERATING SYSTEM OVERVIEW
1.3.4 Scheduling and Resource Management（p66）
 Three factors must be consider
‫ ٭‬Fairness
‫ ٭‬Differential responsiveness(区分服务): e.g. If a process is
waiting for the use of an I/O device, the operating system
may wish to schedule that process for execution as soon as
possible in order to free up the device for later demands
from other processes.
‫ ٭‬Efficiency: Maximize throughput(吞吐量), minimize
response time, accommodate（容纳） as many users as
possible
OPERATING SYSTEM OVERVIEW
Some Concepts（p67）
 Short－term queue
‫ ٭‬Algorithm used to use: round robin（轮转）
 Long－term queue
‫ ٭‬Algorithm used to use: FIFO
 Interrupt handler: the method for get the control
 Service call handler（系统服务处理）: the entry point into
the operating system
OPERATING SYSTEM OVERVIEW
OS
Service Call
Handler
Long-term
Queue
Short-term
Queue
I/O queue
Interrupt
Handler
Short-Term
Scheduler
Fig 2.11 Key elements of an Operating System for Multiprogramming
OPERATING SYSTEM OVERVIEW
System Structure(p68系统结构)
Modules（模块化） structure: only suitable for
small system; for complex system, difficult for
debug
Hierarchical（层） structure
‫ ٭‬Level n provides service for level n+1
OPERATING SYSTEM OVERVIEW
Hierarchy (Table 2.4)
Level Name
Objects
Example Operations
13
Shell
User programming Statements in shell language
environment
12
User processes
User processes
Quit, kill, suspend, resume
11
Directories
Directories
Create, destroy, attach, detach,
search, list
10
Devices
External devices Open, close,
as printer, displays read, write
and keyboards
9
File system
Files
Create, destroy, open, close
read, write
8
Communications Pipes
Create, destroy, open, close,
read, write
OPERATING SYSTEM OVERVIEW
Hierarchy
Level Name
Objects
Example Operations
7
Virtual Memory Segments, pages
Read, write, fetch
6
Local secondary Blocks of data, device
store
channels
Read, write, allocate, free
5
Primitive processes Primitive process,
semaphores, ready
list
Suspend, resume, wait,
signal
OPERATING SYSTEM OVERVIEW
Hierarchy (Hardware)
Level Name
Objects
Example Operations
4
Interrupts
Interrupt-handling
programs
3
Procedures
Procedures, call stack,
display
2
Instruction Set
Evaluation stack, micro- Load, store, add, subtract
program interpreter,
branch
scalar and array data
1
Electronic circuits Registers, gates, buses,
etc.
Invoke, mask, unmask, retry
Mark stack, call, return
Clear, transfer, activate,
complement
OPERATING SYSTEM OVERVIEW
1.4 Characteristics of Modern OS (p71)
1.4.1 Microkernel architecture（微内核结构）
1.4.2 Multithreading（多线程）
1.4.3 Symmetric multiprocess（对称多处理）
1.4.4 Distributed operating systems（分布式系统）
1.4.5 Object-oriented design（对象设计）
OPERATING SYSTEM OVERVIEW
1.4.1 Microkernel
Assigns only a few essential（必要的） functions to
the kernel, including address spaces, interprocess
communication(IPC)（进程间通信）, and basic
scheduling.
Simplifies implementation, provides flexibility（伸
缩性）and well suited to a distributed environment.
OPERATING SYSTEM OVERVIEW
1.4.2 Multithreading
Thread：a dispatchable（分派） unit of work
Process：a collection of one or more threads and
associated（相关） system resources
Introduce thread for improve the concurrence
degree（并发度）
E.g.：a database server accept many connection
request and use multithread for process
OPERATING SYSTEM OVERVIEW
1.4.3 Symmetric Multiprocessing (SMP p73)
 A computer hardware architecture and also to the operating
system behavior that reflects that architecture.
‫ ٭‬Multiple processors
‫ ٭‬These processors share the same main memory and I/O
facilities, interconnected by a bus or other internal
connection scheme.
‫ ٭‬All processors can perform the same functions（hence the
term symmetric）
OPERATING SYSTEM OVERVIEW
SMP vs Single Processor
Performance: parallel and concurrence（并行与并
发）
Reliability/Availability（可靠性/可用性）
Incremental growth（可伸展性）: enhance the
performance of a system by adding an additional
processor
OPERATING SYSTEM OVERVIEW
SMP vs Single Processor (Figure 2.12)
OPERATING SYSTEM OVERVIEW
1.4.4 Distributed Operating System
Data distributed
Task distributed
Transparent（透明）: a multi-processor with a
single processor character
High throughout and reliability
OPERATING SYSTEM OVERVIEW
1.4.5 Object Design
Encapsulation and inherit（封装和继承）
Good scalability（尺度特征）
OPERATING SYSTEM OVERVIEW