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Chapter 6 An Introduction to System Software and Virtual Machines. 國立雲林科技大學 資訊工程研究所 張傳育 (Chuan-Yu Chang ) 博士 Office: ES 709 TEL: 05-5342601 ext. 4337 E-mail: [email protected]. Introduction. - PowerPoint PPT Presentation
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Chapter 6An Introduction to System Software and Virtual Machines
國立雲林科技大學 資訊工程研究所張傳育 (Chuan-Yu Chang ) 博士Office: ES 709TEL: 05-5342601 ext. 4337E-mail: [email protected]
2
Introduction
The computer model, known as Von Neumannmachine described previously is capable ofexecuting programs written in machine language.
However, it lacks “ support tools ” to make theproblem- solving task easy.
A naked machine: hardware loss of any helpful user-oriented features.
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Naked Machines
Need to write the program in 0s and 1s. Need to represented data in binary
form. Need to manually store programs into
memory before executing. Need to instruct the program to start
running …
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User Interface
To make a Von Neumann computer usable, we must create a user interface between user and hardware. Hide from the user the messy and unnecessary details of
the underlying hardware Present information about what is happening in a way that
does not require in-depth knowledge of the internal structure of the system
Allow easy user access to the resource available on this machine
Prevent accidental or intentional damage to hardware, programs, and data
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System Software System Software:
A collection of computer programs that manage the resources of a computer and facilitate access to those resources.
System software acts as an intermediary between the users and the hardware.
The set of services and resources created by the software and seen by the user is called a virtual machine or virtual environment.
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System Software (cont.) The responsibilities of system software
Hide from the user details of the internal structure of the Von Neumann architecture.
Present important information in a way that is easy to understand.
Allow the user to access hardware resources in a simple and efficient way.
Provide a secure and safe environment in which to operate.
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Types of System Software
Operating system, might contain: Language translators: assemblers, compilers. Memory managers
Allocate memory space for programs and data and load programs into memory prior to execution.
File system Handle the storage and retrieval of information on
mass storage devices. Scheduler
Keeps a list of programs ready to run on the processor and selects that will execute next.
Utilities Collections of library routines that provide useful
services either to a user or to other system routines.
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Type of System Software
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Writing a program
Use a text editor to create a program P written in high-level language.
Use the file system to store program P on the hard disk.
Use a language translator to translate program P from a high-level language into a machine language program M.
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Writing a program(cont’d)
Use a loader to allocate sufficient memory to hold program M and load its instructions into memory.
Use the scheduler to schedule and run M. Use a file system to store the output of
program M into data file D. If the program did not complete
successfully, use a debugger to help locate the error.
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Machine Language
Designed from a machine’s point of view, complicated and difficult to understand: It uses binary: no English-like words, mathematical symbols. It allows only numeric memory addresses. It is difficult to change. It is difficult to create data.
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Assembly Language
Designed for people as well as computers Created a more productive, user-oriented
environment One of the most important new
developments in programming Second-generation language More properly viewed as Low-level
programming languages
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Assembly Language (cont’d) Contrast with languages like BASIC, C, C++, Java, which are high-level programming languages. Source program
The programs written by users. Object program
A type of machine language.
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The Continuum of Programming Languages
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Language Translators
The software translate source program (assembly) to object program (machine code) is called assembler( 組譯程式 ).
Translators for high-level programminglanguage are called compilers( 編譯程式 ).
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The translation/Loading/Execution Process
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Advantages of Assembly Language Use of symbolic operation codes rather
than numeric ones. Use of symbolic memory addresses
rather than numeric ones. Data generation, the programmer can
ask the assembler to do data conversion. Pseudo-operations that provide useful
user-oriented services such as data generation.
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Assembly Language Format
Format:label: op code mnemonic address field -- comment
Comment is ignored during translation andexecution.
Op code mnemonic specifies the type ofoperation (Fig. 6.5)
Symbolic labels have two advantages over numeric addresses Program clarity Maintainability
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Typical Assembly Language Instruction Set
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Data Generation using pseudo-op A pseudo-op invokes a service of the
assembler. Can be used to generate data:
. DATA +5 Can be used for program construction:
. BEGIN
. END They do not generate any instructions or data.
將 +5 轉成二進位表示,並且儲存在 memory 中。
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Structure of a Typical Assembly Language Program
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Example of Assembly(Fig. 2.9 sequential search algorithm) LOAD ONE -- put a 1 into register R STORE I -- store the constant 1 into i : : INCREMENT I --add 1 to memory location i : : I : .DATA 0 ONE: .DATA 1
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More Examples Arithmetic expression A=B+C-7 (see
p.249) Conditional operation (see p.249) Looping (see p.250-251) Compute sum of Non-Negative numbers
(see p.253)
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More Examples (Cont.) Arithmetic expression A=B+C-7
LOAD BADD CSUBTRACT SEVEN
STORE A…A: .DATA 0B: .DATA 0C: .DATA 0SEVEN: .DATA 7
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More Examples (Cont.) Conditional operation Input the value of x
Input the value of yIf x>= y then
output the value of xElse
Output the value of y
IN X IN Y LOAD Y COMPARE X JUMPLT PRINTY OUT X JUMP DONEPRINTY: OUT YDONE:…X: .DATA 0Y: .DATA 0
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Figure 6.7Algorithm to Compute the Sum of Numbers
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Figure 6.8 Assembly Language Program to Compute the Sum of Nonnegative Numbers
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Translation and Loading The job of an assembler is to translate a
symbolic assembly language program into machine language. (object file )
The task of a loader is to read instructions from the object file and store them into memory for execution.
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Assembler
An Assembler must perform the following four tasks Convert symbolic op codes to binary Convert symbolic addresses to binary Perform the assembler services requested
by the pseudo-ops Put the translated instructions into a file for
future use.
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Op Code Table The conversion of
symbolic op codes such as LOAD, ADD, and SUBTRACT to binary makes use of a structure called the op code table.
This is an alphabetized list of all legal assembly language op codes and their binary equivalents.
Use binary search to find correspondence.
Operation Binary Value
Structure of the OP code Table
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Symbolic Addresses Conversion After the Op code has been converted into
binary, the assembler must perform a similar task on the address field.
Translation is a two-pass process: First pass: Build the symbol table in the first pass
(Fig. 6.10, 6.11) Looks at every instruction Keeping track of the memory address Determines the address of the label.
Second pass: translate the source program into machine language. (plus handle data generation, produce object file…).(Fig. 6.12.)
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Generation of the Symbol Table假設每個指令和資料均佔 1 byte ,且位址由 0 開始。
前向參考 (forward reference)
DATA 放在 HALT 之後
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Translation and loading (cont.) Binding( 繫結 )
The process of associating a symbolic name with a physical memory address is called binding.
Two primary purpose of the 1st pass To bind all symbolic names to address values To enter those bindings into the symbol table.
Location counter It is using to determine the address where each instruction
will ultimately be stored. The variable used to determine the address of a given instr
uction or piece of data is called location counter.
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Outline of Pass 1 of the Assembler
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Translation and loading (cont.) The responsibilities of pass 2 of the assembler
Translates the source program into machine language. Look up the op code table to translate mnemonic op
codes to binary. Look up the symbol table to translate symbolic addresses
to binary. Handle data generation pseudo-ops Produce the object file
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Fig 6.12 Outline of Pass 2 of the Assembler
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Fig. 6.13 Example of an Object Program
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The Loader
The object program would become input to loader. The loader read instructions from the object file
and store them into memory for execution. When loading is complete, the loader places the
address of the first instruction into the program counter (PC) to initial execution.
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Operating Systems What program examines commands?
System command: may be lines of text typed at a terminal. Point-and-click: menu items displayed on a screen and
selected with a mouse and a button. What piece of system software waits for requests
and activates other system program? The answer is the operating system. Functions of an OS
The user interface System security and protection Encryption Efficient allocation resource The safe use of resource
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The User Interface
The operating system acts like the computer’s receptionist and dispatcher
The OS commands usually request access to hardware resources, software service, or information.
After a command is entered, OS is analyzed to see which software package needs to be loaded and put on the scheduler for execution. (see Fig. 6.15)
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Some Typical Operating System Commands Translate a program Load a translated program into memory Link together separate pieces of software to build a single
program. Run a program Save information in a file Retrieve a file previously stored List all the files for this user Print a file Copy a file from one I/O device to another Establish a network connection Tell me the current time and date
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Figure 6.15User InterfaceResponsibility of theOperating System
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The User Interface (cont.)
Types of the User Interface Prompt character
Command language Graphical user interface, GUI
The GUI supports visual aids and point-and-click operations requiring a mouse, rather than textual commands.
The interface uses icons, pull-down menus, scrolling windows…
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Example of a GUI
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System security and protection OS has the responsibilities of a security guard—cont
rolling access to the computer and its resource. OS must prevent unauthorized users from accessin
g the system and prevent authorized users from doing unauthorized things.
In most OS, access control is handled by requiring a user to enter a legal user name and password before any other requests are accepted .
The password file is maintained by superuser. Encrypt the password file using an encoding algorithm. Encrypted text
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System security and protection (cont.) OS must check to see who is the owner of the file The different levels of operations that various users
may be permitted to do on a file. Read only Append new information to the end of the file but not
change existing information. Changes existing information in the file Delete the entire file from the system
Ex: File GradesName Permitted OperationsSmith R (R=Read only)Jones RA (A=Append)Adams RAC (C=Change)Doe RACD (D=Delete)
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Efficient Allocation of Resources To see that the resources of a computer
system are used efficiently and well Three classes of programs
Running The program currently executing on the processor
Ready Programs that are loaded in memory and ready to run
but are not yet executing. Waiting
Programs that cannot run because they are waiting for an I/O
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The Safe Use of Resource
Not only must resource be used efficiently, they must also be used safely. It is the job of the OS to prevent programs or
users from attempting operations that could cause the computer system to enter a state where it is incapable of doing any further work.
Program A Program BGet the tape drive Get the laser printerGet the laser printer Get the tape drivePrint the file Print the file
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The Safe Use of Resource (cont.) Deadlock
Each program will be waiting for a resource to become available that never will be free.
There is a set of programs each of which is waiting for an event to occur before it may proceed, but that event can be caused only by another waiting program in the set.
Deadlock prevention The OS uses resource allocation algorithms that prevent
deadlock from occurring in the first place. If a program cannot get all the resources that it needs, it must
give up all the resources it currently owns and issue a completely new request.
Deadlock recovery We are powerless to guarantee that deadlock conditions can
never occur. We must detect them and recover from them when they do
occur.
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Summary
The major responsibilities of the OS User interface management Program scheduling and activation Control of access to system and files Efficient resource allocation Deadlock detection, error detection
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Historical Overview of OS development First generation OS (1945-1955)
No OS, there was very little software support (just the assembler and loader)
All machine operation was “hands-on” Second generation OS (1955-1965)
Batch operating system Computer operator groups the programs into a “batch” After a few programs were collected, the operator would
carry this batch of cards to a small I/O computer that would put these programs on tape.
These tapes would be carried into the machine room and loaded onto the “big” computer
Writing the results to another tape.
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Fig. 6.18 Operation of a Batch Computer System
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Fig. 6.19 Structure of a Typical Batch JobBecause programmers no longer operated the machine, they need a way to communicate to the OS what had to be done.
Job control language
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Historical Overview of OS development (cont.)
Command language Job control language Users wrote commands specifying to the OS what operations
to perform on their programs The batch OS kept only a single program in memory at any
one time. Third generation OS(1965-1985)
Multiprogramming Operating Systems There are many user programs simultaneously loaded into
memory. If the currently executing program pauses for I/O, one of the
other ready jobs is selected for execution. Protecting user programs
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Historical Overview of OS development (cont.)
Operating system
Program 1
Program 2
Program 3
Program K
A (upper bound)
B (lower bound)
Multiprogramming Memory Protected
The 3G OS would keep track of the upper and lower address bounds of
each program in memory.
56
Historical Overview of OS development (cont.)
User operation codes That could be included in any user program.
Privileged operation codes Whose use was restricted to the operating system or oth
er system software Eg. HALT instruction
Time-sharing system (1960-1970)
Central ComputerT
T
T TT
T
Telecommunications linkTerminal
57
Historical Overview of OS development (cont.)
compute-bound It does mostly computation and little or no I/O A compute-bound job keeps the processor heavily utilized. To design a time-sharing system, we must make some
change to the multiprogramming OS A program can keep the processor until either of the
following events occurs: It initiates an I/O operation. It has run for a maximum length of time, called a time slice.
The basic idea in a time-sharing system is to service many users in a circular round-robin fashion. Given each user a small amount of time and then moving on
to the next.
58
Historical Overview of OS development (cont.)
The number of simultaneous users that can be serviced by a time-sharing system depends on: The speed of the processor The time slice given to each user The type of operation each user is doing
Single-user OS Gave one user total access to the entire system.
Distributed environment Much of the computing was done remotely in the office. Computing moved out of the computer center to where
the work was being done
59
Historical Overview of OS development (cont.)
The fourth-generation OS (1985-present) Supported both local computation and remote
access to other users and shared resources. Network operating system
The OS Manages not only the resources of a single computer but also the capabilities of a telecommunications system called a local area network (LAN).
LAN is a network that is located in a geographically contiguous area such a room, a building, or a campus.
LAN is composed of PCs, workstations, servers, all interconnected via a high-speed bus.
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Historical Overview of OS development (cont.) There are many shared resources that can
be provided by a network and its OS: File servers
It is a large disk storage facility that is available to any user on the network.
Printer servers Compute server Mail server
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A Local Area Network (LAN)
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Figure 6.22The Virtual Environment Created by a Network Operating System
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Historical Overview of OS development (cont.) Real time operating system
It guarantees that it can service the important requests within a fixed amount of time.
All requests to a real-time OS are prioritized. Embedded system
To place computer inside other pieces of equipment to control their operation.
Eg. Include computers placed inside automobile engines, microwave ovens…
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Historical Overview of OS development (cont.) Fifth Generation OS
Multimedia user interface Parallel processing OS
That will manage systems containing hundreds or even thousands of processors.
Distributed operating system The user does not care where or how the system
satisfies a request as long as it gets done correctly.
65
Historical Overview of OS development (cont.) In a 4G OS, the user issues the following
types of commands Access file F on file server S and copy it to my
local system Run program P on machine M Save file F on file server T Print file F on printer server Q
66
Historical Overview of OS development (cont.) In a distributed OS, the user issues the
following types of commands Access file F wherever it may be Run program P on any machine currently
available Save file F wherever there is sufficient room. Print file F on any printer with 400 dpi resolution
that is not in use right now.
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Figure 6.23Structure of a Distributed System