Operating Systems
OPERATING SYSTEM HANDOUT
SPECIFIC OBJECTIVES:
At the end of the topic session the students are expected to:
Cognitive:
1. Identify the differences between system software and
application software
2. Enumerate the benefits of system software
3. Discuss the different types of system software such as
language translators, interpreters, linkers, and loaders
4. Explain the concept of address binding and the issues
involved
Affective:
1.
2.
Listen to others with respect
Participate in class discussions actively
MATERIALS/EQUIPMENT:
1.
2.
Take home problem set/activities
Projector
TOPIC PREPARATION:
o
Consult the reference book for further reading.
TOPIC PRESENTATION:
The topic will revolve around introduction to system software
and system programming. Discussions will include
introduction to system programming, types of system
programs, and address binding.
This will be the suggested flow of discussion for Introduction
to System Software and System Programming.
1. Introduce system software and system programming.
2. Explain the relationship and differences between system
software and application software.
3. Discuss the types of system programs and its uses.
4. Explain the concepts of address binding and the
techniques involved in the process.
The questions below will help you thoroughly discuss the
lesson.
Guide Questions:
a. Give examples of other basic operations of a computer
system.
b. What are the advantages of using high-level languages?
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c.
Introduction
Differentiate the three address binding techniques.
Introduction
Software is defined as a program or set of instructions that
tells the computer what to do. Programming languages such
as C++ and Java are used to write the instructions.
There are two classes of software: system software and
application software.
System Software
These programs are used to manipulate the basic operations
of a computer system. Examples of these basic operations
are:
System software tells the computer to accept the input
from the keyboard and output the character to the monitor.
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System software locates free disk space in a hard disk
when a file needs to be saved. It writes the file to the hard
disk and modifies the disk directory system to record the
existence of the file.
System software sends the document to the printer when
it needs to be printed. It also tells the printer how it should
be printed.
System software locates a program in the hard disk, loads
it in the main memory, and executes it.
Note that the user does not need to know the exact details of
how these tasks are performed. The system software takes
care of these exact details.
Some of the benefits of system software are:
They hide the “ugly” details of computer operations from
the user. It creates a virtual machine interface where
the user does not need to know how the computer works
on the hardware level.
Computer programmers can write programs without
knowing the details on how the computer hardware works.
It makes programming easier since programmers do not
need to know about how to control the hardware. They
can write programs using C++ and Java and use system
software (compiler) to convert it to a language that is
understandable by the computer.
System software such as an operating system controls the
execution of programs. Several programs can be
executed at the same time, thus increasing CPU
productivity and efficiency.
Examples of system software: operating systems,
communication control programs, interpreters, compilers,
debuggers, text editors, linkers, loaders.
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Since system software controls the operation of computer
hardware, they are obviously machine dependent. System
software programmers should have a strong knowledge of the
architecture of the computer hardware they are using.
System software supports all application programs. For
example, a user using an application program such as
Microsoft Word clicks on the save icon to tell Word to save a
document. In this process, Word does not communicate with
the printer, but rather requests the operating system to print
the document. A block diagram of this process is illustrated in
the figure below.
Introduction
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How System Software Supports Application Software
Application Software
These programs are used to accomplish specialized tasks for
computer users. These tasks are related to professional and
personal needs of the user such as creating documents,
sending e-mail, editing photographs, playing games, browsing
the Web, drawing, creating database, etc.
Software that falls into the category of application programs
are:
Document production software – These are programs that
are used to compose, edit, print, and electronically publish
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Operating Systems
documents. Examples of this are word processing
software (Microsoft’s Word and OpenOffice.org’s Writer),
desktop publishing software (Microsoft’s Publisher and
Adobe’s PageMaker), and Web authoring software
(Microsoft’s FrontPage and Macromedia’s Dreamweaver).
Software that falls into the category of application programs
are:
Document production software – These are programs that
are used to compose, edit, print, and electronically publish
documents. Examples of this are word processing
software (Microsoft’s Word and OpenOffice.org’s Writer),
desktop publishing software (Microsoft’s Publisher and
Adobe’s PageMaker), and Web authoring software
(Microsoft’s FrontPage and Macromedia’s Dreamweaver).
Spreadsheet software – These are programs that are
used to create and manipulate spreadsheets electronically
for analysis, planning, and modeling. Examples of this are
Microsoft’s Excel and OpenOffice.org’s Calc.
Presentation software – These are programs that are
used to create and display information in the form of slide
shows. Examples of this are Microsoft’s PowerPoint and
OpenOffice.org’s Impress.
Database management software – These are programs
that are used to store, modify, and retrieve information
from a database in an organized and structured manner.
Examples of this are Microsoft’s Access and
OpenOffice.org’s Base.
Business software – These are programs that can provide
users with tools for business management. Examples of
this are finance software (Microsoft’s Money and Reilly’s
Moneydance),
accounting
software
(Peachtree’s
Accounting), tax preparation (Quicken’s Turbo Tax), etc.
Multimedia software – These are programs that can
manipulate picture, sound, and video. Examples of this
are image editing software (Adobe’s Photoshop and
Corel’s Photo-Paint), audio editing software (Adobe’s
Audition and Sony’s Sound Forge), and video editing
software (Adobe’s Premiere and Autodesk’s Maya).
Entertainment software – Examples of this are music
players (Nullsoft’s Winamp and Media Science’s
Sonique), video players (Microsoft’s Media Player and
CyberLink’s PowerDVD), games (Blizzard’s WarCraft and
Valve’s Counter-Strike), etc.
[Introduction, Pages 1 to 4 of 11]
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Operating Systems
Introduction to System
Programming
Page 5 of 11
Introduction to System Programming
System programming is simply the act of developing system
software. As mentioned before, system programmers should
have a strong knowledge of the architecture of the computer
hardware they are using.
System software can be written in machine language.
Machine language is the natural or primitive language that
the computer actually understands. It is a low-level language
which consists of 0’s and 1’s and the only language a machine
understands. Thus, it is very difficult to program.
Programs written in machine language are very fast and
efficient, which are very important characteristics for system
software. However, programming in this language is very
tedious and highly prone to errors. For these reasons,
machine language programming is no longer done.
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System software can also be written in assembly language.
Assembly language uses abbreviations or mnemonics in
place of binary patterns. Mnemonics are easier to remember,
thus make programming easier.
Before a computer can execute an assembly language
program, it should be first converted to machine language
program. A system software called assembler is a special
translator program that translates assembly language
mnemonics into machine language instructions. Assembly
language programming is very popular in system software
development because of its acceptable level of efficiency.
Lastly, system software can be written in high-level
programming language.
High-level
programming
languages are easy to use because it uses English-like
commands. Examples of this software are C++, Java, and
Visual Basic.
Before a computer can execute high-level programming
language instructions, it should be first converted to machine
language program. A system software called compiler is a
special translator program that converts high-level language
instructions into machine language.
Advantages of high-level languages over assembly language:
High-level programming languages are easier to learn and
use.
Most high-level programming languages have pre-defined
functions and subroutines, thus make programming
easier. For example, C++ has built-in mathematical
functions.
High-level programming languages in general, are not
machine-dependent. For example, the instruction set of
Java can be used for both Intel-based and Motorolabased computers, with little or without modifications.
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Advantages of assembly language over high-level languages:
The assembly language program executable code is
compact. A compact or short code would mean that the
program can execute faster. Most compilers of high-level
programming languages are not optimized to create a
compact code.
Assembly language is not constrained with certain
programming conventions nor rigid coding restrictions.
Assembly language has instructions that allow
programmers more direct control over memory access.
Some system software programmers use assembly languagebased subroutines to supplement the high-level programming
language capabilities.
[Introduction to System Programming, Pages 5 to 6 of 11]
Types of System
Programs
Types of System Programs
Language Translators
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These system programs convert a high-level language
program or assembly language program into machine
language.
The two types of language translators are:
1. Assemblers – language translator that convert a program
written in assembly language into an executable file
containing machine language instructions
2. Compilers – language translator that convert a program
written in high-level language into an executable file
containing machine language instructions
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Some compilers first produce files that contain instructions in
an intermediate language, which can then be recompiled to
machine language instructions.
Interpreters
These system programs convert a high-level language
program into machine language. Unlike
compilers,
interpreters read one instruction from the source code, convert
it to machine language, and then execute it before proceeding
to the next instruction. It also does not generate an
executable file.
Each instruction must be translated each time they are read.
As a result, interpreted programs run much slower than
compilers.
Examples of interpreted programming languages are BASIC,
Perl, and JavaScript embedded in HTML pages.
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Types of System
Programs
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Linkers and Loaders
As mentioned earlier, high-level programming languages have
pre-defined functions and subroutines. A collection of these
functions and subroutines can be found in the library.
Programmers can use these libraries to enhance the
functionality of their programs.
This means that a program is composed of the main program
and the subprograms or routines. This program may be a part
of a much bigger system, wherein modular programming is
practically implemented. In modular programming, a large
program is divided into several modules which is created,
compiled, and tested separately. After the process, these
modules and the routines of the library must be combined.
Some compiler does not generate the final executable file
immediately. Each program is first converted to an object file
or object module (which contains machine language
instructions) and then combined with other programs using a
linker. The linker (link editor or linkage editor) is a system
software that combines or links the modules together with the
libraries which then form a single executable program called
the load module. Below is a diagram of this process.
The Linking Process
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Another system software called loader is the one responsible
for bringing the load module to the main memory for
execution. Its main function is to perform address binding.
Address Binding
[Types of System Programs, Pages 7 to 9 of 11]
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Address Binding
Symbolic variables are used to represent data in a program.
Any name can be used but it is recommended to use a
variable name that represents the data it will store. Examples
of variable names are gross_sales, interest, age, first_name,
etc.
Variables are assigned specific locations in the main memory
when the program is compiled and loaded into the main
memory for execution. Each main memory location has a
unique numeric address. For example, the variable cost may
be assigned to a memory location whose address is 1045.
Any reference or changes to the value of gross_sales in the
program will refer or reflect in the contents of memory location
1045. The figure below illustrates this process.
memory
addresses
1043
1044
1045
1000
1046
gross_sales = 1000;
.
.
.
.
.
.
.
.
.
.
gross_sales = 2000;
.
.
1047
1048
1049
Main
Memory
1043
1044
1045
2000
1046
1047
1048
1049
Program
Since the program
initialized the value of
gross_sales to 1000, the
contents of memory
location 1045 will be
equal to1000
Main
Memory
At this point in the
program, the value of
gross_sales was
changed to 2000.
Therefore, the contents
of memory location
1045 will be changed to
2000
Assignment of Variables to Memory Locations
The memory locations to be assigned for symbolic variables
depend on the available free memory space when the
program is loaded. The process of assigning or mapping
symbolic references to actual memory locations is referred to
as address binding. The actual main memory location is
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Address Binding
called physical address or absolute address.
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Calls for subroutines and functions can also be given symbolic
variables, hence, address binding can also be
done.
Example: A program contains a subroutine compute_grade
which is loaded in main memory 3000. Assume that the
command to invoke this subroutine is call compute_grade.
When the main program is loaded into the main memory, the
call compute_grade command will change to jump 3000
command. The call compute_grade command becomes a
reference to memory location 3000 which is the start of
compute_grade subroutine.
The loader may use three techniques in placing the load
module in main memory. These are: absolute loading,
relocatable loading, and dynamic run-time loading.
Absolute Loading
In absolute loading, the load module has actual memory
addresses assigned instead of symbolic variables. The actual
addresses may have been determined before or during
compile time. The load module is placed into main memory
without performing address binding.
This method may not be a problem in a computer system with
only one program running at any given time. Problems might
occur in a multiprogrammed system where two or more
programs may be running at the same time and sharing the
same main memory space. Delays may arise if for example, a
program needs to be loaded, but the assigned memory space
is occupied by another program. In this case, the programmer
should assign a new memory space then recompile it to
generate a new load module.
Relocatable Loading
In relocatable loading, address binding is performed right
before the load module is loaded and the address assignment
is based on the available main memory location at that time.
The address that will be generated is referred to as relative
address. The relative address is based on a reference point
or base address. For example, a relative address is 200
memory locations from the start of the program. If the
program is loaded at memory location 500, then the absolute
address is 500 + 200 = 700. If the start of the program is
relocated to memory location 800, a new absolute address will
be computed by the loader. The new absolute address is 800
+ 200 = 1000.
In general,
absolute address = r + x
wherein r is the memory location from the reference point and
x is the reference point.
The relative or relocatable addresses must be generated
during compile or assembly time of the load module. All the
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relative addresses and information on the reference point is
contained in a relocation dictionary of the load module.
Since the relative addresses become absolute addresses
when loaded, the program cannot be moved to a different
memory once it starts executing. This becomes a problem in
some situation wherein programs need to be relocated to
maximize the use of CPU and main memory. It can only be
moved by terminating the program and reloading it so that
new absolute addresses can be generated.
Dynamic Run-Time Loading
This technique is used in most modern operating systems. In
dynamic run-time loading, the absolute address is not
generated when loaded, but only when it is needed by the
CPU. It places the load module in main memory but does not
convert the relative addresses to absolute addresses.
Relocating a program becomes possible even though it is
executing.
Since the absolute address is computed during run-time, the
problem is execution time will definitely slow down. This can
be avoided using special hardware to speed-up the
conversion process which will be discussed in the succeeding
lessons.
[Address Binding, Pages 10 to 11 of 11]
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