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CSCI-235
Micro-Computer in Science
System Software
System Software

System software includes all of the programs
needed to keep a computer and its peripheral
devices running smoothly
 Two major categories of system software are:


Operating systems
System utilities
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The Operating System

The operating system (OS) is a set of programs
that perform certain basic functions with a
specific type of hardware

The functions of the OS are:

Starting the computer

Managing programs

Managing memory

Handling messages from input and output devices

Enabling user interaction with the computer
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The Operating System

OS stays behind the scenes
 All software depends on the OS
Sales
Summary
Income
Statement
Office
Inventory
CAD
GUI
Operating
System
Tax
Planning
Human
Resource
Mgt.
Loan
Computer
Evaluation
Games
System Investment
System
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Operating Systems for Large
Computers
 Resource

Assigning computer resources to certain
programs and processes for their use
 Main




allocation
issues related to resource allocation
Sharing the Central Processing Unit (CPU)
Sharing memory
Sharing storage resources
Sharing printing resources
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Sharing the CPU
 Multiprocessing
 Multiprogramming
 Time-Sharing
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Multiprocessing
 The
use of a powerful computer with
multiple CPUs
 Multiple

programs run simultaneously
Each runs on its own processor
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Multiprogramming
 Two
or more programs executed
concurrently


Programs take turns using the CPU
Event-driven
• An interrupt suspends processing to allow another
program to run
• After the second program runs, the OS returns the
CPU to another program
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Time-Sharing

Programs take turns using the CPU
 Time-driven



Each user is given a slice of time (fraction of a second)
CPU works only on that user’s tasks during his/her time
slice
Typically used in applications with many users
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Starting the Computer
– The process of loading or
reloading the OS into the computer’s
memory
 Booting
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Starting the Computer
 The
computer copies the kernel from the
hard drive into the computer’s memory

The kernel
•
•
•
•
•
Is the central part of the OS
Starts all applications
Manages devices and memory
Resides in memory at all times
Performs other essential functions
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Managing Programs

Single-tasking systems run one application
program at a time

Multitasking OSs have the ability to run more
than one application program at a time

Multitasking is accomplished by

A foreground application
• The active program or program in use

One or more background applications
• Inactive program(s) or program(s) not in use
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Example of Multitasking
Background
application
Foreground
application
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Storage Structure

Programs must be in main memory (RAM) to execute
 Von-Neumann architecture
 Load instruction from memory into instruction register
 Operands fetched from memory to internal registers
START
Fetch next instruction from
Memory to IR
Increment PC
Decode and Execute
Instruction in IR
NO
STOP ?
YES
Storage Structure


Ideally, we want programs and data to reside in main
memory permanently
 Main memory is usually too small
 Main memory is volatile – loses contents on power loss
Secondary storage holds large quantities of data,
permanently
 Magnetic disk is the most common secondary-storage
device

Actually, a hierarchy of storage varying by speed, cost,
size and volatility
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Storage-Device Hierarchy
Storage Technology

Static RAM (SRAM)


Dynamic RAM (DRAM)


50ns – 70ns, $20 – $75 per GB
Magnetic disk


0.5ns – 2.5ns, $2000 – $5000 per GB
5ms – 20ms, $0.20 – $2 per GB
Ideal memory


Access time of SRAM
Capacity and cost/GB of disk
Managing Memory
 The
operating system allocates memory
areas for each running program; it keeps
programs from interfering with each other
 The
operating system uses virtual memory
as an extension of random access
memory (RAM)
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Managing Virtual Memory
hard disk
page
swapped
in
most recently
transferred data or
program instructions
memory
Virtual memory
management
swap
file
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page
swapped
out
least recently
used data or
program instructions
Virtual Memory and Cache
Cache/VM: Analogy

You are going to do some research on a particular
topic. Thus, you go to the library and look for the a
shelve that contains books on that particular topic

You pick up a book from the shelve, find a chair, seat
and start reading
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Cache/VM: Analogy

You find a reference to another book on the same topic
that you are also interested in reading. Thus, you stand
up, go to the same shelve, leave the first book and pick
up the other book

Then, you go back to the chair and start reading the
second book

Later on you realize that you want to read the first book
once again (or another related book). Thus, you repeat
the same process (i.e., go to the shelve to find it)
© Prentice-Hall, Inc
Cache/VM: Analogy

Suppose that instead of taking just one book from the
shelve, you take 10 books on the same topic. Then,
you find a table with a chair, put the 10 books on the
table, sit there and start reading one of the books

If you need another related book, there is a good
chance that it is on your table so you don’t have to go
to the shelve to get it. Also, you can leave the first
book on the table and there is a good chance that you
will be needing it again later
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Handling Input and Output
 Input
and output devices generate interrupts,
or signals, that tell the operating system that
something has happened
 The
OS provides interrupt handlers or miniprograms that begin when an interrupt
occurs
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Providing the User Interface

The user interface is that part of the OS
with which the user interacts with a
computer
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Types of User Interfaces

Graphical user interface (GUI)




Menu-driven


Uses graphics to create a desktop environment
Icons (small pictures) represent computer resources
Programs run within on-screen windows
Text-based menus are used to show all of the
options available to the user
Command-line

The user is required to type keywords or commands
in order to enter data or give instructions
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Graphical User Interface (GUI)
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Menu-driven User Interface
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Command-Line Interface
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Popular Operating Systems
MAC OS
WINDOWS XP
UNIX
MS-DOS
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LINUX
Microsoft Windows
Click to view each Windows version (1985-2001)
Windows
Windows
Windows
Windows
Windows
Windows
3.x2000
ME
NT
XP
2.0
95
98
(1990-1992)
1.0(1998)
(1995)
(2001)
(1993)
(1987)
(2000)
(1985)
(2000)
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MAC OS

Created in 1984

First OS to use
graphical user
interface

Easiest operating
system for
beginners

Mac OS X, was
released in 2000
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MS-DOS

Developed for IBM PCs in
1981

Uses command-line
interface

Use is diminishing
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UNIX
 Developed
by AT&T
in 1970s
 Developed
concepts
of file management
and path names
 Widely
used by
corporations
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 Developed
in
1991 by UNIX
 Open-source
code –Available
for all to see and
use
 More
stable than
Windows
 Powerful
and free
 Growing
acceptance
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Linux
System Utilities: Tools for
Housekeeping

System utilities are programs that help the
operating system manage the computer
system’s resources

Types of utilities

Backup software

Antivirus software

Disk scanning

Disk defragmentation

File management

File-searching software

File compression
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Backup Software

Backup software includes programs that
enable the user to copy data from the hard
disk to another storage medium
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Antivirus Software
 Antivirus
software protects the computer
from computer viruses
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File Management Utilities
 Known
as a file manager
 Enables
the user to perform
various tasks on storage
devices using files, folders,
and directories

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Tasks include:

Creating folders

Saving, deleting, copying,
and moving files and folders

Examining the contents of
files

Launching application
programs
Search
 Search
programs enable users to find files
on storage devices
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File Compression Utility
A
file compression utility reduces the size
of a file
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Troubleshooting
 Computer

Use a boot disk (emergency disk) in the
floppy drive
 System


startup failure
slowdown
Scan for viruses
Defragment the hard disk
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