system structure in operating systems.pdf

Operating System Structure
(UNIT-1)
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CH N V MALLIKHARJUNA RAO

1. Simple Structure.
2. Layered Approach.
3. Micro kernals.
4. Modules.
5. Hybrid Systems.
⚫
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⚫ A system as large and complex as a complex as a modern
operating system must be engineered carefully if it is to
function properly and be modified easily.
⚫ A common approach is to partition the task into small
components ,or modules ,rather than have one monolithic
system.
⚫ Each of these modules should be a well defined portion of
the system ,which carefully defined inputs ,outputs and
functions.
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Simple Structure
⚫ Many Operating Systems do not have well-defined
Structures , frequently ,such systems started as small
,simple ,and limited systems and then grew beyond their
scope. MS-DOS is an example of such a system.
⚫ It was originally designed and implemented by a few
people who had no idea that it would become so popular.
⚫ It was written to provide the most functionality in the least
space , so it was
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Simple Structure
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Simple Structure
⚫ UNIX – limited by hardware functionality, the original
UNIX operating system had limited structuring. The
UNIX OS consists of two separable parts.
⚫ Systems programs
⚫ The kernel
⚫ Consists of everything below the system-call interface and above
the physical hardware
⚫ Provides the file system, CPU scheduling, memory management,
and other operating-system functions; a large number of functions
for one level.
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Traditional UNIX System Structure
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Layered Approach
⚫ With proper hardware support, operating systems can be
broken into pieces that are smaller and more appropriate
than those allowed by the original MS-DOS and UNIX
systems.
⚫ The operating system can then retain much greater control
over the computer and over the applications that make use
of that computer. Implementers have more freedom in
changing the inner workings of the system and in creating
modular operating systems.
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Layered Approach
⚫ An operating-system layer is an
implementation of an abstract object made up
of data and the operations that can manipulate
those data.
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• A system can be made modular in many ways.
One method is the layered approach, in which
the operating system is broken into a number of
layers (levels).

Layered Operating System
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Layered Approach
⚫ The main advantage of the layered approach is simplicity
of construction and debugging.
⚫ The layers are selected so that each uses functions
(operations) and services of only lower-level layers. This
approach simplifies debugging and system verification.
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Layered Approach
⚫ The first layer can be debugged without any concern for the
rest of the system, because, by definition, it uses only the basic
hardware (which is assumed correct) to implement its
functions.
⚫ Once the first layer is debugged, its correct functioning can be
assumed while the second layer is debugged, and so on.
⚫ If an error is found during the debugging of a particular layer,
the error must be on that layer, because the layers below it are
already debugged. Thus, the design and implementation of the
system are simplified.
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Layered Approach
⚫ Each layer is implemented only with operations provided
by lower-level layers. A layer does not need to know how
these operations are implemented; it needs to know only
what these operations do. Hence, each layer hides the
existence of certain data structures, operations, and
hardware from higher-level layers.
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Layered Approach
⚫ A final problem with layered implementations is that they tend
to be less efficient than other types.
⚫ For instance, when a user program executes an I/O operation,
it executes a system call that is trapped to the I/O layer, which
calls the memory-management layer, which in turn calls the
CPU-scheduling layer, which is then passed to the hardware.
⚫ At each layer, the parameters may be modified, data may need
to be passed, and so on. Each layer adds overhead to the
system call. The net result is a system call that takes longer
than does one on a non layered system.
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Layered Approach
⚫ The operating system is divided into a number of layers
(levels), each built on top of lower layers. The bottom
layer (layer 0), is the hardware; the highest (layer N) is the
user interface.
⚫ With modularity, layers are selected such that each uses
functions (operations) and services of only lower-level
layers.
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Layered Approach
⚫ The major difficulty with the layered approach involves
appropriately defining the various layers. Because a layer
can use only lower-level layers, careful planning is
necessary.
⚫ For example, the device driver for the backing store (disk
space used by virtual-memory algorithms) must be at a
lower level than the memory-management routines,
because memory management requires the ability to use
the backing store.
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Layered Approach
⚫ A layered design was first used in the operating system.
Its six layers are as follows:
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Layered Approach
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Microkernals
⚫ This method structures the operating system by removing all
nonessential components from the kernel and implementing
them as system and user-level programs. The result is a smaller
kernel.
⚫ The main function of the microkernel is to provide
communication between the client program and the various
services that are also running in user space. Communication is
provided through message passing.
⚫ Kernel is system software which is part of operating
system. Operating System provides interface b/w user and
hardware. kernel provides interface b/w application and
hardware. It also provides protection and security.
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Microkernals
⚫ In the mid-1980s, researchers at Carnegie Mellon
University developed an operating system called Mach
that modularized the kernel using the microkernel
approach.
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Architecture of a typical microkernel.
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Methods of communication
⚫ Simplex (One way of Communication) –TV ,RADIO.
⚫ Half Duplex(One way at a time)- Walkie -Talkie
⚫ Full Duplex(two way Communication) –TELEPHONE
⚫ COMMUNICATION IS OF TWO TYPES
⚫ GUIDED
⚫ UNGUIDED
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Methods of communication
⚫ Simplex (One way of Communication) –TV ,RADIO.
⚫ Half Duplex(One way at a time)- Walkie -Talkie
⚫ Full Duplex(two way Communication) –TELEPHONE
⚫ COMMUNICATION IS OF TWO TYPES
⚫ GUIDED
⚫ UNGUIDED
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Microkernals
1. One benefit of the microkernel approach is that it makes
extending the operating system easier.
2. All new services are added to user space and
consequently do not require modification of the kernel.
3. When the kernel does have to be modified, the changes
tend to be fewer, because the microkernel is a smaller
kernel.
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Microkernals
⚫ The microkernel also provides more security and
reliability, since most services are running as user—rather
than kernel— processes. If a service fails, the rest of the
operating system remains untouched
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Architecture of Micro kernel
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Modules
⚫ Here, the kernel has a set of core components and links in
additional services via modules, either at boot time or
during run time. This type of design is common in modern
implementations of UNIX, such as Solaris, Linux, and
Mac OS X, as well as Windows.
⚫ Linux also uses loadable kernel modules, primarily for
supporting device drivers and file systems.
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Solaries Loadable Modules
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Micro kernals
⚫ The Solaris operating system structure, shown in the
above Figure is organized around a core kernel with seven
types of loadable kernel modules:
1. Scheduling classes
2. File systems
3. Loadable system calls
4. Executable formats
5. STREAMS modules
6. Miscellaneous
7. Device and bus drivers
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Hybrid Systems
⚫ In practice, very few operating systems adopt a single,
strictly defined structure. Instead, they combine different
structures, resulting in hybrid systems that address
performance, security, and usability issues. For example,
both Linux and Solaris are monolithic, because having the
operating system in a single address space provides very
efficient performance. However, they are also modular, so
that new functionality can be dynamically added to the
kernel.
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Hybrid Systems
⚫ Windows is largely monolithic as well, but it retains some
behavior typical of microkernel systems, including
providing support for separate subsystems that run as
user-mode processes. Windows systems also provide
support for dynamically loadable kernel modules.
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Hybrid Systems
⚫ The three hybrid systems: the Apple Mac OS X operating
system and the two most prominent mobile operating
systems—iOS and Android.
⚫ Mac OS :
1. The Apple Mac OS X operating system uses a hybrid
structure.
2. The top layers include the Aqua user interface and a set
of application environments and services.
3. the Cocoa environment specifies an API for the
Objective-C programming language, which is used for
writing Mac OS X applications.
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Hybrid Systems( Mac OS )
⚫ Below these layers is the kernel environment, which
consists primarily of the Mach microkernel and the BSD
UNIX kernel.
⚫ Mach provides memory management; support for remote
procedure calls (RPCs) and inter -process communication
(IPC) facilities, including message passing; and thread
scheduling.
⚫ The BSD component provides a BSD command-line
interface, support for networking and file systems.
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Hybrid Systems( Mac OS )
⚫ Below these layers is the kernel environment, which
consists primarily of the Mach microkernel and the BSD
UNIX kernel.
⚫ Mach provides memory management; support for remote
procedure calls (RPCs) and inter -process communication
(IPC) facilities, including message passing; and thread
scheduling.
⚫ The BSD component provides a BSD command-line
interface, support for networking and file systems.
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Hybrid Systems -iOS
1. iOS is a mobile operating system designed by Apple to
run its smart phone, the iPhone, as well as its tablet
computer, the iPad.
2. iOS is structured on the Mac OS X operating system,
with added functionality pertinent to mobile devices, but
does not directly run Mac OS X applications
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Hybrid Systems- Android
1. The Android operating system was designed by the
Open Handset Alliance (led primarily by Google) and
was developed for Android smart phones and tablet
computers.
2. Whereas iOS is designed to run on Apple mobile
devices and is close-sourced, Android runs on a variety
of mobile platforms and is open-sourced, partly
explaining its rapid rise in popularity.
3. Android is similar to iOS in that it is a layered stack of
software that provides a rich set of frameworks for
developing mobile applications.
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The Mac OS X structure
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Architecture of Apple’s iOS.
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Architecture of Google’s Android
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Thank You
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system structure in operating systems.pdf

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system structure in operating systems.pdf