Title: Invitation to Computer Science 5th Edition
1 Invitation to Computer Science 5th Edition
- Chapter 6
- An Introduction to System Software and
Virtual Machines
2Objectives
- In this chapter, you will learn about
- System software
- Assemblers and assembly language
- Operating systems
3Introduction
- Naked machine
- Hardware bereft of any helpful user-oriented
features - Data as well as instructions must be represented
in binary - To make a Von Neumann computer usable
- Create an interface between the user and the
hardware
3
4 System Software
- The virtual machine
- System software collection of computer programs
that manage the resources of a computer and
facilitate access to those resources - Software sequences of instructions that solve a
problem
4
5Figure 6.1 The Role of System Software
6 Types of System Software
- Operating system
- Communicates with users
- Determines what they want
- Activates other system programs, applications
packages, or user programs to carry out their
request
7Types of System Software (continued)
- User interface
- Provides user with an intuitive visual overview
- Language services (assemblers, compilers, and
interpreters) - Allow you to write programs in a high level
- Memory managers
- Allocate memory space for programs and data
- Information managers
- Handle the organization, storage, and retrieval
of information on mass storage devices
8Figure 6.2 Types of System Software
9 Types of System Software (continued)
- I/O systems
- Allow you to easily and efficiently use the input
and output devices that exist on a computer
system - Scheduler
- Keeps a list of programs ready to run on the
processor and selects the one that will execute
next - Utilities
- Library routines that provide useful services
either to a user or to other system routines
10 Assemblers and Assembly Language
- Problems with machine language
- Uses binary
- Is difficult to change
- Is difficult to create data
11 Assembly Language
- Assembly language
- Low-level programming language
- Each symbolic assembly language instruction is
translated into exactly one binary machine
language instruction - High-level programming languages
- User oriented
- Not machine specific
- Use both natural language and mathematical
notation in their design
12Figure 6.3 The Continuum of Programming Languages
13 Assembly Language(continued)
- Source program
- Program written in assembly language
- Object program
- Source program must be translated into a
corresponding machine language program - Assembler
- System software that carries out translation
- Advantage of assembly language
- Allows use of symbolic addresses
14Figure 6.4 The Translation/ Loading/Execution
Process
15Figure 6.5 Typical Assembly Language Instruction
Set
16 Assembly Language(continued)
- Advantages of symbolic labels
- Program clarity
- Maintainability
- Pseudo-op
- Invokes the service of the assembler
- Provides program construction
17Figure 6.6 Structure of a Typical Assembly
Language Program
18 Examples of Assembly Language Code
- Conditional operation
- Tests and compares values
- Algorithmic problem-solving cycle
- One of the central themes of computer science
19Figure 6.7 Algorithm to Compute the Sum of Numbers
20Figure 6.8 Assembly Language Program to Compute
the Sum of Nonnegative Numbers
21 Translation and Loading
- Assembler
- Translates a symbolic assembly language program
into machine language - Tasks performed
- 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
22 Translation and Loading (continued)
- Op code table
- Alphabetized list of all legal assembly language
op codes and their binary equivalents - In assembly language
- A symbol is defined when it appears in the label
field of an instruction or data pseudo-op - Pass
- Process of examining and processing every
assembly language instruction in the program, one
instruction at a time
23Figure 6.9 Structure of the Op Code Table
24Figure 6.10 Generation of the Symbol Table
25 Translation and Loading (continued)
- First pass over source code
- Assembler looks at every instruction
- Binding
- Process of associating a symbolic name with a
physical memory address - Primary purposes of the first pass of an
assembler - To bind all symbolic names to address values
- To enter those bindings into the symbol table
26 Translation and Loading (continued)
- Location counter
- Variable used to determine the address of a given
instruction - Second pass
- Assembler translates source program into machine
language - After completion of pass 1 and pass 2
- Object file contains the translated machine
language object program
27Figure 6.11 Outline of Pass 1 of the Assembler
28Figure 6.12 Outline of Pass 2 of the Assembler
29Figure 6.13 Example of an Object Program
30 Operating Systems
- Operating system
- Waits for requests and activates other system
programs to service these requests - System commands
- Used to translate, load, and run programs
31 Functions of an Operating System
- The user interface
- Operating system commands usually request access
to hardware resources, software services, or
information - To communicate with a user, a GUI supports visual
aids and point-and-click operations
32Figure 6.14 Some Typical Operating System
Commands
33Figure 6.15 User Interface Responsibility of the
Operating System
34Figure 6.16 Example of a Graphical User Interface
35 System Security and Protection
- Operating system
- Controls access to the computer and its resources
- Safeguards password file
- Sometimes uses encryption to provide security
- Access control
- Use of a legal user name and password
36Figure 6.17 Authorization List for the File GRADES
37 Efficient Allocation of Resources
- I/O controller
- Frees the processor to do useful work while the
I/O operation is being completed - To ensure that a processor does not sit idle if
there is useful work to do - Operating system keeps a queue of programs that
are ready to run
38 The Safe Use of Resources
- Operating system
- Prevents programs or users from attempting
operations that cause the computer system to
enter a frozen state - Deadlock
- Each program is waiting for a resource to become
available that will never become free
39 The Safe Use of Resources (continued)
- Deadlock prevention
- Operating system uses resource allocation
algorithms that prevent deadlock from occurring
in the first place - Deadlock recovery algorithms
- Detect and recover from deadlocks
40 Summary of OS Responsibilities
- Major responsibilities of operating systems
- User interface management (a receptionist)
- Control of access to system and files (a security
guard) - Program scheduling and activation (a dispatcher)
- Efficient resource allocation (an efficiency
expert) - Deadlock detection and error detection (a traffic
officer)
41 Historical Overview of OperatingSystems
Development
- First-generation system software
- Roughly 19451955
- No operating systems and very little software
support - Second-generation system software
- Called batch operating systems (19551965)
- Command language
- Commands specifying to the operating system what
operations to perform on programs
42Figure 6.18 Operation of a Batch Computer System
43Figure 6.19 Structure of a Typical Batch Job
44Historical Overview of OperatingSystems
Development (continued)
- Third-generation operating systems
- Multiprogrammed operating systems (19651985)
- Many user programs are simultaneously loaded into
memory - User operation codes could be included in any
user program - Privileged operation codes use restricted to the
operating system or other system software
45Historical Overview of OperatingSystems
Development (continued)
- Time-sharing system
- Many programs can be stored in memory
- Allows programmer to enter system commands,
programs, and data online - Distributed environment
- Much of the computing was done remotely in the
office, laboratory, classroom, and factory - Network operating system
- Fourth-generation operating system (1985present)
46Figure 6.20 Configuration of a Time-Shared
Computing System
47Figure 6.21 A Local Area Network
48Historical Overview of OperatingSystems
Development (continued)
- Real-time operating system
- Manages resources of embedded computers that are
controlling ongoing physical processes - Guarantees that it can service important requests
within a fixed amount of time
49The Future
- Multimedia user interfaces
- Will interact with users and solicit requests in
a variety of ways - Parallel processing operating system
- Can efficiently manage computer systems
containing tens, hundreds, or even thousands of
processors - Distributed computing environment
- Users do not need to know the location of a given
resource within the network
50Figure 6.23 Structure of a Distributed System
51Figure 6.24 Some of the Major Advances in
Operating Systems Development
52 Summary
- System software
- Acts as an intermediary between the users and the
hardware - Assembly language
- Creates a more productive, user-oriented
environment than machine language - An assembler
- Translates an assembly language program into a
machine language program