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Week 9a
What is an Operating System?
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A computer consists of Software (Programs) and
Hardware (CPU, Memory, Motherboard etc). The
operating system is a software component of a
computer system that manages all the hardware and
software. It controls every file, every device,
allocation of processing time and memory. It controls
who can use the system and how.
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Operating System Software
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Every operating system performs four essential
functions. Memory management, processor
management, Device management and file management.
Each function is carried out with the respective manager
Memory manager, Processor Manager, Device manager
and File manager. Each of the processor must perform
the following tasks
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Monitor its resources continuously
Apply policies on how each resource is allocated and to whom
Allocate the resources that is handling
Deallocate the resources when needed
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Kernel
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Kernel is the core of the operating system. It resides in
main memory at all times and performs the most
essential tasks such as managing memory, process
scheduling etc
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User Command interface
 Every operating system provides an interface that
accepts commands from the operator. This interface
can be in the form of a command-line interface or in
the form of a Graphical User Interface (GUI).
Command line interfaces were very common on early
systems and UNIX systems. GUI (Windows)
interfaces are widespread used on Apple and Windows
operating systems.
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Types of operating systems
 Operating systems can be distinguished into five
categories based on their response time and how the
data is entered in to the system.
 Batch Systems :
 In a batch system programs to be run were collected in a designated
area, read onto a magnetic tape using a small, relatively inexpensive
computer. After collecting jobs in this manner for a prescribed
period of time, the tape was rewound and mounted on a tape drive
connected to the main computer where the programs were run one
after the other. The output from each program was collected onto a
second tape. When the entire batch was processed, the operator
removed both tapes and passed the one with the outputs on to be
printed by the same small computer connected to a printer. The
operator then mounted another tape with another batch of programs
to be run.
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Types of operating systems
 Interactive Systems
 Interactive systems are a variation of multiprogramming
systems because they allow several users to be on-line at the
same time. The computer can provide fast interactive
service to several users, and programmers can debug their
programs in a shorter period of time than was possible with
batch systems. This is because not all users are issuing
commands to the computer at the same time. For example,
of 300 users logged on there may be only 20 percent
actively working at any given time allowing the CPU to
handle their requests in a timely manner. In addition, some
of the commands may take a small amount of CPU time to
complete, for example to compile a student program, while
others may take a longer time to finish, thus balancing the
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workload.
Types of operating systems
 Real Time Systems
 Real-time systems are used in time critical environments
such as vehicle control or patient monitoring where failures
in the system could lead to loss of life or major destruction
of property. They are usually considered dedicated systems
which spend most of the time on a single job. Work such as
laboratory experiment monitoring, or environment control
within buildings requires continuous processing, with little
opportunity to use the computer for unrelated purposes.
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Types of operating systems
 Hybrid Systems
 Hybrid Systems are a combination of batch and Interactive
systems. Batch jobs are running the background when the
interactive activity is low. They are utilizing system
resources efficiently.
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Types of operating systems
 Embedded Systems
 Embedded systems are computers systems that are placed
inside other devices. They have all the main components of
a computer system (CPU, memory) but are performing
specific functions to enhance the functionality of the device.
They can only run specific programs and they make very
efficient use of their limited resources.
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Desktop and server Operating systems
 Operating systems can be classified based on
the users’ accessibility into Desktop operating
systems and Server operating Systems.
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Desktop Operating systems
 Desktop Operating systems are used on single user
systems. They are used on personal computers that
perform general tasks such as writing documents and
internet browsing. Examples of Desktop operating
systems are Windows XP, Windows 7, Linux Ubuntu
desktop edition.
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Server Operating systems
 Server operating systems are used on multiuser
systems. Many users can access the system
concurrently via the network. They perform functions
such as File sharing, mail servers, web servers,
application servers. Examples of server operating
systems are Windows Server 2008, UNIX and IBM
Mainframes.
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Device management
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The Device Manager is in charge of monitoring the
device connected to the Computer systems such as disk
drives, printers, ports etc. It allocates and deallocates
these resources to the running process based on
scheduling policy.
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