An operating system (OS) is software that controls hardware and facilitates interaction between users and applications. Types of OS include real-time, single-user/single-tasking, single-user/multitasking, and multi-user/multitasking systems, each serving different user needs and computing environments. Auxiliary utilities enhance OS capabilities, including backup, antivirus, firewall, and intrusion detection software, with primary OS examples being Microsoft Windows, UNIX, and Linux.

1. OPERATING SYSTEMS
Operating system (OS) – is a software program that controls the system’s hardware and that
interacts with the user and application software. OS is the computer’s master control program.
OS also acts as the primary controlling mechanisms for the computer’s hardware.
Functions of Operating Systems:
• Provide a user interface – displays the on-screen-elements with which you interact.
• Run programs - loads programs into the computer’s memory so that you can use them.
• Manage hardware devices – coordinates how programs work with the computer’s
hardware and other software.
• Organized file storage – manages the way information is stored on and retrieved from
disks.
Types of Operating Systems:
1. Real-Time Operating Systems – very fast, relatively small OS. Real-time OSs are
often embedded OSs, built into the circuitry of a device and are not loaded from a disk
drive. Real-time OS is needed to run real-time applications; it may support multiple
tasks, or it may only support single-tasking.
Real-time application – an application that responds to certain inputs extremely quickly
—thousandths or millionths of a second (milliseconds or microseconds, respectively).
Real-time applications are needed to run medical diagnostics equipment, life-support
systems, machinery, scientific instruments, and industrial systems.
2. Single-User/Single-Tasking Operating Systems – allows a single user to perform just
one task at a time. To a user, a task is a function such as printing a document, writing a
file to disk, or editing a file. To OS, a task is a process, and small and simple OSs can
only manage a single task a time. Take up little space on disk and run on inexpensive
computers.
Example of a single-tasking OS: MS-DOS, Palm OS used on the Palm handheld
computers.
3. Single-User/Multitasking Operating Systems – allows a single user to perform two or
more functions at once. It takes a special OS to keep two or more tasks running a once.
Require expensive computers and tend to be complex.
Examples: MS Windows, Macintosh OS
4. Multi-User/Multitasking Operating Systems – allows multiple users to use programs
that are simultaneously running on a single network server, called a terminal server.
This gives each user a complete environment, called user session, on the server. Each
user’s applications run within their user session on the server separate from all other
user sessions. The software that makes this possible is called a terminal client.
Advantage: maintenance can be easy and allow user to work with applications that
require a more powerful computer.
Disadvantage: if network connection to the server is broke, the user cannot work in the
applications on the server.
Examples: UNIX, VMS, mainframe OS (MVS)

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3. User Interface – on-screen elements that enable the user to interact with the software.
Two most common types of user interfaces:
1. Graphical User Interface (GUI) – a user interface in which actions are initiated when
the user selects an icon, a toolbar button, or an option from a pull-down menu with the
mouse or other pointing device.
– Most common interface used in Windows, OS X, Gnome, KDE
2. Command-Line Interface – a user interface that enables the user to interact with the
software by typing strings of characters at a prompt.
– Older interface - DOS, Linux, UNIX
Running Programs
The operating system provides a consistent interface between application programs and the
user. It is also the interface between those programs and other computer resources such as
memory, printer, or another program.
System call – a feature built into an application program that requests a service from the
OS, as when a word processing program requests the use of the printer to print a
document. Provides consistent access to OS features.
Services that an OS provides to programs:
o Saving the contents of files to a disk.
o Reading the contents of a file from disk into memory.
o Sending resources that let you copy or move data from one document to another
or from one program to another.
o Allocating RAM among the running programs.
o Recognizing keystrokes or mouse clicks and displaying characters or graphics on
the screen.
Sharing Information between programs
o Copy and paste
o Object Linking and Embedding
Managing Hardware
When programs run, they need to use the computer’s memory, monitor, disk drives, and other
devices, such as a printer. The operating system is the intermediary between programs and
hardware.
Processing Interrupts – the OS uses interrupt requests (IRQs) to help coordinate
processes.
Working with Device Drivers – the OS often provides programs for working with
special devices such as printers. These programs are called drivers because
they allow the OS and other programs to activate and use—that is, “drive”—the
hardware device.
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4. Enhancing an OS with Utility Software
Utilities – are software programs that enhance or extend the operating system’s capabilities, or
that simply offer new features not provided by the OS itself.
Popular utilities:
1. Backup Utilities – backup utility can help you copy large groups of files from your hard
disk to another medium. Many newer OS feature built-in backup utilities but feature-rich
backup software is available from other sources. These utilities not only transfer files to
a backup medium, they also organize files, update backups, and restore backups to disk
in case of data loss.
2. Antivirus – a virus is a parasitic program that can delete or scramble files or replicate
itself until the host disk is full. Antivirus utility can examine the contents of a disk or
RAM for hidden viruses and files that may act as hosts for virus code.
3. Firewall – an antipiracy method for protecting networks. A firewall permits access to
public sections of the network while protecting propriety areas.
4. Intrusion Detection – while firewall offers protection form predictable intrusion.
Intrusion detection software reveals the types of attacks a firewall is thwarting, creating
logs of the attempts notifying you of certain types of intrusion attempts.
5. Screen Savers – popular utilities, although they serve little purpose other than to hide
what would otherwise be displayed on the screen. Screen savers display a moving
image on the screen and were originally created to prevent displayed images from
“burning” into the monitor.
PC Operating Systems:
• Microsoft Windows is the most popular
– Installed more than other OS combined
– Installed on about 95% of computers
– Apple and Linux represent the other 5%
• DOS (Disk Operating System)
– Single user single-tasking OS
– Command line interface
– 16-bit OS
– Powerful
– Fast
– Supports legacy applications
• Windows NT
– Designed for a powerful system
– 32-bit OS
– Very stable
– Windows NT Workstation – single-user multitasking OS
– Windows NT Server
• Multi user multi tasking OS
• Network operating system
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5. • Windows 9x
– 95, 98, and Millennium Edition (Me)
– 32-bit OS
• Supported 16-bit programs well
– unstable OS
– Still found in large corporations
– 95 introduced the Start button
– 98 introduced active desktop, inclusion of Internet Explorer Web browser
– Windows Me (Millenium Edition) improved multimedia capabilities, built-in support for
digital video editing, and enhanced Internet features.
• Windows 2000 Professional
– Combines user-friendly interface and features of Windows 98 with file system,
netwoking,
power and stability of Windows NT
– Optimized for office and developers
– Application software ran very well
– Support symmetric multiprocessing (SMP) with up to two processors
• Windows XP
– Microsoft’s newest desktop product
– Different look from 2000
– Many different versions
– Digital multimedia support was enhanced
– Communications was enhanced
– Mobile computing became a priority
– Takes advantage of universal Plug and Play support
• UNIX
– Runs on all computer types
– 32- or 64-bit
– Very stable and fast
– Command-line interface
– Can cost thousands of dollars
• Linux
– Free or inexpensive version of UNIX
– 32-bit OS
– Very stable and fast
– Most flavors are open source
– X Windows GUI
• Command line interface is available
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6. • Macintosh operating systems
– OS X
– Based on FreeBSD Linux
– Very stable and easy to configure
– Only runs on Mac hardware
Network Operating System – is an OS that is designed to run on a network server dedicated
to providing various services to other computers on the network.
Network Operating System Features:
• Fast and stable
• Runs on servers
• Multi-user and multitasking OS
• 32- or 64-bit
• File and print sharing
– Users access the same files
– Hundreds of users use a printer
– Different OS can interact
• Data integrity
– Backups copies data onto tape
– RAID copies data onto other drives
• Redundant Array of Inexpensive Disks (RAID)
• Relies on two or more hard drives
• May speed access to data
• Data security
– Access to data can be restricted
– Access to server resources is controlled
– Audits can be kept
• NT Server
– Same core as NT Workstation
– Security added
– Multi user capability added
– RAID support included
• Windows 2000 Server
– Same technology as 2000 workstation
– Active Directory (AD)
• Central database of server resources
• Simplifies network management
– Distributed programs supported
– Server Standard Edition
– Advanced Server Edition
– Data Center Edition
• Windows 2003 Server
– Designed to compete with UNIX
– XP like interface
– Better support for XP computers
– MS .NET framework supported
– Distributed programs are supported
– Server Standard Edition
– Data Center Edition – database center
• UNIX for servers
– Oldest NOS in widespread use
– Stable secure and fast
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7. – Main OS for Internet and Web
– Large organizations depend on UNIX
• Linux for servers
– Popular in small businesses
– Stable, fast and inexpensive
– Linux’s popularity is growing
Embedded Operating Systems – is one that is built into the circuitry of an electronic device.
• Cell phones, PDAs, medical equipment
• Stable and fast
• Windows XP embedded
– Based on Windows XP
– Customized for each device
• Windows CE
– Not based on a desktop OS
– Customized for each device
– PDA and cell phones
– Microsoft Automotive will run in cars
• Palm OS
– Standard on Palm PDA
– First PDA OS for consumers
– Can be found on cell phones
• Pocket PC
– Developed to compete with Palm
– Not customizable
– Interacts securely with business networks
– Can control PCs through PC
• Symbian
– Found in smart cell phones (Nokia, Sony Ericsson)
– Games, Instant Messaging, Internet
– Full color display
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