Operating systems

OPERATING SYSTEMS
S . K AT H E E S K U M A R .
H . D I P. I N . I N F O R M AT I O N T E C H N O LO G Y

INTRODUCTION
• An operating system (OS) is the software component of a
computer system that is responsible for the management
and coordination of activities and the sharing of the
resources of the computer. The OS acts as a host for
application programs that are run on the machine.

WHAT IS AN OPERATING SYSTEM?
• The most important program that runs on your computer. It
manages all other programs on the machine.
• Every PC has to have one to run other applications or
programs. It is the first thing “loaded”

WHY OPERATING SYSTEM?
• It performs basic tasks, such as:
• Recognizing input from the keyboard or mouse,
• Sending output to the monitor,
• Keeping track of files and directories on the disk, and
• Controlling peripheral devices such as disk drives and printers.

TYPES OF OPERATING SYSTEMS
• Generally, there are four types, based on the type of computer they
control and the sort of applications they support.
• Single-user, single task
– This type manages the computer so that one user can effectively do one thing
at a time.

• Multi-user, multi-task
– Allows two or more users to run programs at the same time. Some
operating systems permit hundreds or even thousands of concurrent
users.

• Real Time Operating Systems
– RTOS are used to control machinery, scientific instruments, and
industrial systems.
– There is typically very little user interface capability. Resources
are managed so that a particular operation executes precisely the
same every time.

• Single-user, Multi-tasking
– This is the type of operating system most desktops and laptops
use today.
– Microsoft’s Windows and Apple’s MacOS are both examples of
operating systems that will let a single user have several
programs in operation at the same time.

OS’S MANAGE APPLICATIONS
• Operating systems provide a software platform on top of which other
“application” programs can run.
– The application programs must be written to run on a particular
operating system.
– So, your choice of operating system determines what application
software you can run.

OPERATING SYSTEM FUNCTIONS
• Besides managing hardware and software resources on the system,
the OS must manage resources and memory.
– There are two broad tasks to be accomplished.

OS - MEMORY STORAGE AND
MANAGEMENT
• Each process must have enough memory in which to execute, and
• It can neither run into the memory space of another process,
• Nor be run into by another process.

RAM MEMORY
• Random access memory (RAM) is the best known form of computer
memory. •
• RAM is considered "random access" because you can access any
memory cell directly if you know the row and column that intersect at
that cell
• The more RAM your computer has, the faster programs can
function. The two main types are called DRAM and SRAM. SRAM
is faster than DRAM, but, more expensive.

OS - WAKE UP CALL
• When you turn on the power to a PC, the first program that runs is a set
of instructions kept in the computer's read-only memory (ROM).

OS - WAKE UP CALL
• It checks to make sure everything is functioning properly.
• It checks the CPU, memory, and basic input-output systems (BIOS) for
errors
• Once successful, the software will begin to activate the computer's
disk drives.
• It then finds the first piece of the operating system: the bootstrap
loader.

OS - BOOTING THE PC
• The bootstrap loader is a small program that has a single function: It loads the
operating system into memory and allows it to begin operation.
• The bootstrap loader sets up the small driver programs that interface with and
control the various hardware.
• It sets up the divisions of
– memory •
– user information, and
– applications.

OS - BOOTING THE PC
• It establishes the data structures needed to communicate within and
between the subsystems and applications of the computer.
• Then it turns control of the computer over to the operating system.

WINDOWS AND MAC ARE GUI’S
• Microsoft Windows and Apple Macintosh operating systems are “graphical user
interfaces” or GUI’s.
• GUI is defined as: A picture used in place of a word or words to issue commands.
• GUI interfaces have standards that are usually the same or similar in all systems
and applications.
• Standards apply to:
– Pointers and pointing devices
– Icons, desktops, windows and menus

Operating systems

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