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Project on :Time Sharing

File ManagementOperating System Structure

Submitted by:Name – Mayank GargRoll No. – 47Batch - Morning

Submitted to:Miss Priyanka Kapoor

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File Management:

File AccessFile Operation

Time Sharing:

RequirementAdvantages & DisadvantagesOS

Structure:

Layered StructureKernelMono Lithic KernelMicro Lithic KernelDifference

Operating System Module

INDEX

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Time Sharing System

• Time-sharing is the sharing of a computing resources among many users by means of multiprogramming and multi-tasking.

• It extended the idea of multiprogramming to allow multiple terminals with each-in-use terminal to be associated with one or more jobs.

• Hence, there are spaces for more than one user, each associated with a program or more.

• Time-sharing dramatically lowered the cost of providing computing capability, made it possible for individuals and organizations to use a computer without owning one.

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The main idea of time sharing systems is to allow a large number of users to interact with a single computer (system) concurrently.

It uses multi programming with a special CPU scheduling algorithm to achieve it.

The main objective of these systems is to minimize the response time to user commands.

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requirements

Connection of several terminals with the system so that multi user can interact in interactive mode.

Large memory to support multiprogramming. Memory protection mechanism to prevent

interaction/accessing of multi users in multiprogramming environment.

An alarm clock mechanism to send an interrupt signals to the CPU after every time interval.

Job status preservation mechanism. Special CPU scheduling algorithm.

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Reduce CPU idle time.Offer good computing facility to small users.Provides advantages of quick response.CPU is used most effectively of the time.

Time delay as it might get over loaded as many users are working on single system and output will be displayed late.

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File Management

Data stored in secondary storage disk is in form of file which provides long term storage.

A file is collection of related information defined by its creator. E.g. – magnetic tapes/disk, optical disk, etc.

File management module of an operating system takes care of file related activities such as structuring, accessing, naming, sharing, and protecting.

Major activities are- creation & deletion of files & directories, mapping of file, backup of files on stable storage media, support primitives for manipulating files & directories.

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File Access MethodAn access method is a function of a mainframe open rating system that enables access to data on disk, tape or other external devices.

It is supported by sequential access and random access.

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• The direct-access method is based on a disk model of a file, since disks allow random access to any file block.

• Random files are not transportable

• We cannot peek inside then with an editor

• Or type them in meaningful way to screen

Random Access Method

• It is the group of data in the memory array or a disk file or on a tape which is accessed in a predetermined order.

• One start at the beginning of the file and work through each record in turn.

• Important advantage of sequential files is that different records can have different lengths; the minimum record length is zero but the maximum is system-dependent.

Sequential Access Method

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FILE OPERATIONS It helps in dealing with files and its content. Create Delete Open Close Read Write Seek Rename Copy Get & Set Attributes

Attributes like read-only hidden system and archive.

11OperatingSystemStructure

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Layered StructureIt attempts to achieve

robustness by structuring the architectures into layers with different privileges.

Contemporary operating system, do not use the layered design as it too restrictive and requires specific hardware support.

Modern operating system- organize their components into number of layers each built in top of its lower layers.

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The layer is selected such that each layer uses the functions and services provided by its intermediate lower layers.

Bottom layer is the hardware.Top layer is the user interface.The main advantage is modularity.This approach greatly signifies the design and

implementation of the system because each layer is implemented using only those operations provided by its immediate lower level layers.

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KERNEL The kernel is the main

component of most computer operating systems.

It is a bridge between applications and the actual data processing done at the hardware level.

The kernel's responsibilities include managing the system's resources.

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FACILITIES OF KERNEL1. The kernel takes responsibility for deciding at

any time which of the many running programs should be allocated to the processor or processors.

2. The kernel is responsible for deciding which memory each process can use, and determining what to do when not enough is available.

3. The kernel allocates requests from applications to perform Input/output to an appropriate device and provides convenient methods for using the device.

4. Key aspects necessary in resource managements are the definition of an execution domain and the protection mechanism used to mediate the accesses to the resources within a domain.

5. Kernels also usually provide methods for synchronization and communication between processes called inter-process communication (IPC).

6. A kernel may rely on some of the processes it runs to provide the facilities to other processes,

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MONOLITHIC KERNEL All OS services runs along

with the main kernel thread, also residing in the same memory.

It provides powerful hardware access.

A monolithic kernel is one single program that contains all of the code necessary to perform every kernel related task.

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Advantages: Since there is less software involved it is faster. As it is one single piece of software it should be smaller

both in source and compiled forms. Less code generally means fewer bugs which can

translate to fewer security problems.

Limitations: Coding in kernel can be challenging, Rebooting the computer is often needed. A bug in one function can corrupt data structure, part of the

kernel, or running programs. Difficult to maintain. Even if the modules servicing these operations are separate

from the whole, the code integration is tight and difficult to do correctly.

Since the modules run in the same address space, a bug can bring down the entire system.

They are not portable; that is, they must be rewritten for each new operating system.

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MICRO LITHIC KERNEL

A microkernel that is designed for a specific platform or device is only ever going to have what it needs to operate.

The microkernel approach consists of defining a simple abstraction over the hardware, with a set of primitives or system calls to implement minimal OS services such as memory management, multitasking, and inter-process communication.

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Advantages: Maintenance is easier. Patches can be tested in a separate instance, and then

swapped in to take over a production instance. Rapid development time and new software can be tested

without rebooting the kernel. More persistence. Most micro kernels use a message passing system of some sort

to handle requests from one server to another.

Disadvantages: Larger running memory footprint More software for interfacing is required, there is a potential

for performance loss. Messaging bugs can be harder to fix due to the longer trip

they have to take versus the one off copy in a monolithic kernel.

Process management is very complicated. They are extremely context based.

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Difference Monolithic & Micro Lithic Kernels Monolithic kernel is a single large processes running entirely in a single address space.

Monolithic kernel is a large program, which contains different modules and they can interact each other .

New modules can be dynamically linked or inserted in it.

We do not want to reboot the system.

The examples of monolithic kernel based OSs are Linux, Unix.

Micro kernel is broken down into separate processes, known as servers.

Micro lithic kernel contains different modules which are linked together .

These modules can communicate with those modules ,which are linked with it.

We have to link it with other modules to whom with which it has to communicate.

The example of microkernel based OS are Mac OS X and Windows NT

Operating System Module

Those module of an operating system that are always kept in the system’s main memory due to limited memory capacity in the hard disk are called resident module.

Criteria determining whether the operating system should be resident :

Those module that are kept on the hard disk are called non resident modules.

These modules are loaded into the memory on demand, that is, as and when they are needed for execution.

• Its frequency of use• Whether the system can

operate at all with out it.

Resident ModuleNon-Resident Module

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Bibliography • http://www.wikipedia.com/• ICAI ITT Module-1, page no.: 55 – 59, August 2011

edition• http://en.wikipedia.org/wiki/Kernel_(computing)#

Monolithic_kernels• http://

wiki.answers.com/Q/Difference_between_monolithic_and_microlithic_kernel