Transcript System Software

CS 1308 Computer Literacy and the Internet
SYSTEM SOFTWARE
Introduction
 Von Neumann computer
 “Naked machine”
 Hardware without any helpful user-oriented
features
 Extremely difficult for a human to work with
 An interface between the user and the
hardware is needed to make a Von Neumann
computer usable
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System Software: The Virtual
Machine
 System software
 Acts as an intermediary between users and
hardware
 Creates a virtual environment for the user that
hides the actual computer architecture
 Set of services and resources created by the
system software and seen by the user
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Figure 6.1
The Role of System Software
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BIOS
 Basic Input/Output System
 The first piece of software that starts when the
computer is turned on
 Stored in Flash Memory
 Power-on Self-test (POST) makes sure that all the
system components are running properly (e.g.
RAM check)
 Gets the keyboard, mouse, and other peripherals
started
 Finds the “Boot” device and starts the operating
system
 For more information (Google “How does the BIOS
work”)
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Types of System Software
 System software is a collection of many
different programs
 Operating system
 Controls the overall operation of the computer
 Communicates with the user
 Determines what the user wants
 Activates system programs, applications
packages, or user programs to carry out user
requests
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Functions of an Operating
System
 Five most important responsibilities of the
operating system
 User interface management
 Program scheduling and activation
 Control of access to system and files
 Efficient resource allocation
 Deadlock detection and error detection
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The User Interface
 Operating system
 Waits for a user command
 If command is legal, activates and schedules the
appropriate software package
 Types of User interfaces
 Text-oriented – DOS, Unix, Linux
 Graphical – Mac, Windows, Linux
 Hybrid – Cell phones, digital cameras, PDAs
 Embedded –Microwave ovens, cars, etc.
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System Security And
Protection
 The operating system must prevent
 Unauthorized people from using the computer
 User names and passwords
 Legitimate users from accessing data or
programs they are not authorized to access
 Authorization lists
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0
An OS provides security, e.g. against
viruses!
Microsoft Word
The virus code overwrites
other programs in memory.
Microsoft Word
Doom
the virus code
Doom
DOS OS
DOS OS
Shareware Game
16M
When an “infected program”
is run, the program counter
(PC)
might take the value of the
first address of the virus code.
Should this happen, the
virus code will be executed.
Memory How might the OS prevent this?
Shareware Game
Memory
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Efficient Allocation Of Resources
 The operating system ensures that
 Multiple tasks of the computer may be underway at
one time
 Processor is constantly busy
 Keeps a “queue” of programs that are ready to run
 Whenever processor is idle, picks a job from the
queue and assigns it to the processor
 Memory and secondary storage devices are
used efficiently.
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An OS Allocates Resources
Efficiently:
 It’s easy for an OS that supports a single user running a
single program
Doom
Word
Windows
Netscape
JAVA
SPSS
disk
bus
ALU
PC
registers
memory
CPU
Peripherals:
•monitors
•printers
•network connections
•etc.
1. User tells OS to execute program
2. OS finds the program on disk
3. OS copies the program into memory
4. OS initializes the PC to the beginning of the program
5. Program monopolizes all computer resources
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This wastes computer
resources
 Input and Output are very slow
 Disk and peripherals are 10,000x slower than
the CPU
 The user (typing on the keyboard) is even
slower!
 CPU time is wasted while waiting for them
 During this time, CPU could be executing
other programs!
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Multitasking
 Although it seems like your computer is
running many programs at once, including
the OS, it is not.
 Your computer runs a bit of one program
before switching to another.
 And then switching again, often because it is
waiting for I/O.
 Because your computer is very fast, it seems
like they are all running at the same time.
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The Future
 Operating systems will continue to evolve
 Possible characteristics of fifth-generation systems
 Multimedia user interfaces
 Parallel processing systems
 Completely distributed computing environments – possibly
over the internet (cloud computing)
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Summary
 System software acts as an intermediary
between the users and the hardware
 Your computer would be useless without an
operating system and system software.
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