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Sunday, January 31, 2010

Definition of Operating System

A type of system software that underlies all other software.
It manages all software and hardware tasks.
It provides a common set of computer functions such as input from a keyboard and output to a monitor.
It provides the user interface……that is:
How can something as simple-minded as a processor and memory present you with something as rich as the Mac or Windows GUI?

Provides user interface ...as we saw.
Allows applications to run.
What are some tasks you need done even when no apps are running?
Does nearly half of what we ask an application program to do!
Common tasks useful to all programs —put those in the OS (the most basic are put in BIOS) so each app doesn’t have to handle those tasks.
So what are some of these tasks?


Reads from and writes to the I/O devices.
In the past, application programmers had to write control programs for I/O devices. Painful!

Today, O.S. reads from and writes to the I/O devices: mouse, keyboard, printer, monitor
About half the instructions in today’s OS are to manage input and output operations

EXAMPLES of I/O operations

OS reads mouse movement and writes to display screen.
You move the mouse---what do you expect to happen?
What that involves…
Manage interrupt.
OS reads mouse wheels.
OS draws cursor arrow (changes pixel colors so arrow appears to be “moving”).

OS identifies selected objects on the desktop

You select an icon--what do you expect to see?
What that involves…!
FIRST: you move the cursor to point to icon…
Draws “moving cursor…”
OS keeps table of icon placements…
Looks at current cursor placement and compares it to that table.
NEXT: you single-click mouse button to SELECT it:
What do you expect to see?
OS does all this!

Manages files and folders
You Create a new file or folder
You Move files and folders; you “nest” folders
You Open a document file… whoa! Let’s see:
OS looks at file extension
OS checks if enough free memory space
OS finds and loads the APP (if not loaded)
OS finds and loads the document
OS keeps track of what data goes with what program (all sharing same RAM)
OS turns control over to the APP

What do you do with files and folders…cont’d
You Start an app from Start Menu ...
You Copy a file or a folder.
You Print a file.
You Save, or Save As (see FAT, later) …
You Exit from an app

User file management and viewing tools are provided by OS: SUCH AS?
My Computer
Windows Explorer

Many universal file management operations [under File menu] are done by OS:
New, Open, Close, Save, Save As, Print, Exit…
Again, great for users: Consistency!

Digression: Disk & file management is critical!
OS keeps track of disk drives by assigning names
Windows OS: uses letters (A, B, C, D, …..)
During disk formatting: each track & sector is labeled, and the FAT is created.
FAT: log that contains location (cluster #) of each filename. (FAT is updates each time a file is created, moved, renamed, or deleted.

Misc Services and Utilities

OS does system control ops from Start button:
Shut down; Restart.
OS does universal ops from the Edit menu:
Cut, Copy, Paste, Clear, Select All
Clipboard … (also between different apps

Difference between a simple copy/paste, and OLE = object linking & embedding

OS does universal ops from the View menu:
Show/Hide Toolbars & Status bar;
Large icons, Small icons;
List; Details;
Arrange Icons; etc.

Translators (revisited!)

How do people write programs?
Only language a computer understands?
A translator (or compiler):
Program that converts high-level source code into low-level machine language (object code)-- can then be processed directly by the computer’s binary circuits.
Running a source program is a two-step process:
Execute the translator program first:
converts ASCII source into executable machine language
creates a new file containing the object code.
Execute that NEW object code file.

OS Capability
Operating systems can be classified as follows:
-multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.

-multiprocessing : Supports running a program on more than one CPU.

-multitasking : Allows more than one program to run concurrently. multithreading : Allows different parts of a single program to run concurrently.

-real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

Example Popular OS
For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.

Software Piracy

Making illegal copies of copyrighted software
Why the fuss?
Very easy to duplicate software vs. a text book
Software company may lose hundreds of dollars per pirated copy
Yes: Small-medium sized business who purchase a few copies and distribute to many users
No: Individual users who probably would not have purchased software on their own anyway


Software is copied onto CD-ROMS / DVD-ROMS
Package duplicates the original
Sold in flea markets or small stores
Cheaper price
Occurs more overseas

Copying Software
Legitimate reasons
Backup copy
Copy to hard disk
Illegitimate reasons
Obtain software without paying for it

Open Source Software

Open source software (OSS) began as a marketing campaign for free software.
OSS can be defined as computer software for which the human-readable source code is made available under a copyright license (or arrangement such as the public domain) that meets the Open Source Definition.
This permits users to use, change, and improve the software, and to redistribute it in modified or unmodified form. It is very often developed in a public, collaborative manner.

Open source software is the most prominent example of open source development and often compared to user generated content
Examples of open source licenses include Apache License, BSD license, GNU General Public License, GNU Lesser General Public License, MIT License, Eclipse Public License and Mozilla Public License.


Freeware is computer software that is available for use at no cost or for an optional fee.
Freeware is often made available in a binary-only, proprietary form, thus making it distinct from free software
Proprietary freeware allows authors to contribute something for the benefit of the community, while at the same time allowing them to retain control of the source code, future direction of development and preserve its business potential.
Freeware is different from shareware, where the user is obliged to pay (e.g. after some trial period or for additional functionality).

The only criterion for being classified as freeware is that the software must be fully functional for an unlimited time with no cost, monetary or otherwise.
The software license may impose restrictions on the type of use including personal use, individual use, non-profit use, non-commercial use, academic use, commercial use or any combination of these.
For instance, the license may be "free for personal, non-commercial use".
Everything created with the freeware programs can be distributed at no cost (for example graphics, documents, or sounds made by user).

This is a list of freeware video games implemented as traditional executable files that must be downloaded and installed.
Freeware games are games that are released as freeware and can be downloaded and played, free of charge, for an unlimited amount of time and may be redistributed.
List of open source games
F.E.A.R. Combat (2006) is the multiplayer portion of F.E.A.R., by Monolith Productions
SimCity (1989), a City-building game, was released under the GPLv3 for the One Laptop per Child project, and as Micropolis to the general public (the original title of the game).

popularized by Bob Wallace
refers to copyrighted commercial software that is distributed without payment on a trial basis and is limited by any combination of functionality, availability, or convenience.
Shareware is often offered as a download from an Internet website or as a compact disc included with a periodical such as a newspaper or magazine.
The aim of shareware is to give buyers the opportunity to use the program and judge its usefulness before purchasing a licence for the full version of the software.

is usually offered as a trial version with certain features only available after the licence is purchased, or as a full version, but for a trial period.
Once the trial period has passed the program will not run until a licence is purchased.
Shareware is often offered without support, updates, or help menus, which only become available with the purchase of a licence.
The words "free trial", "trial version" are indicative of shareware.

Free/open source software and shareware are similar in that they can be obtained and used without monetary cost.
Usually shareware differs from free/open source software in that requests of voluntary shareware fees are made, often within the program itself, and in that source code for shareware programs is generally not available in a form that would allow others to extend the program.
Notwithstanding that tradition, some free/open source software authors ask for voluntary donations, although there is no requirement to do so.
Free/open source software is usually compatible with the strict Association of Shareware Professionals shareware guidelines.
large online distribution channels known as "portals", such as Download.com, Tucows, Yahoo! Games and RealArcade emerged years.
These portals acted as media of distribution for the shareware developers, providing a much larger audience than before.

Software Licence

A software license is a legal instrument governing the usage or redistribution of copyright protected software.
A typical software license grants an end-user permission to use one or more copies of software in ways where such a use would otherwise constitute infringement of the software publisher's exclusive rights under copyright law.
In effect, the software license acts as a promise from the software publisher to not sue the end-user for engaging in activities that would normally be considered exclusive rights belonging to the software publisher.

Software licenses grant rights to users which would otherwise be prohibited by copyright.
These include rights on usage, modification and redistribution.
Several open source software licenses have qualified within the boundary of the Open Source Definition.
The most prominent example is the popular GNU General Public License (GPL).
Software licenses can generally be fit into one of two distinct categories:
proprietary licenses
open source licenses.
The features that distinguish the two forms of licensing are significant in terms of the effect they have on the end-user's rights.

Proprietary software licenses
The hallmark of proprietary software licenses is that the software publisher grants a license to use one or more copies of software, but that ownership of those copies remains with the software publisher (hence use of the term "proprietary").
One example of such a proprietary software license is the license for Microsoft Windows.

Open source licenses

With open source licenses, in contrast to proprietary software licenses, ownership of a particular copy of the software does not remain with the software publisher.
Instead, ownership of the copy is transferred to the end-user.
As a result, the end-user is, by default, afforded all rights granted by copyright law to the copy owner.
Note that "copy owner" is not the same as "copyright owner".
While ownership in a particular copy is transferred, ownership of the copyright remains with the software publisher.
An example of an open source license is the GNU General Public License (GPL).
This license is aimed at giving the end-user significant permission, such as permission to redistribute, reverse engineer, or otherwise modify the software.
These permissions are not entirely free of obligations for the end-user, however.
The end-user must comply with certain terms

(Sumber rujukan KUIN/INTERNET)

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