TYBsc Comp Sci

8/7/2019 TYBsc Comp Sci

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STRUCTURED SYSTEM ANALYSIS AND

DESIGN BY PROF YK


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March 16, 2011 By Prof YKSIDDHIVINAYAK CLASSES

2

UNIT THREE


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DESIGNING THE APPLICATION ARCHITECTURE1. It consists of application software programs that will carry out the function of the

system.

2. Application design must be done in the conjunction with the design of the database.

3. Application design must be done in the conjunction with the design of the user

interface.


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SYSTEM FLOW CHART

1. It is an diagram that describes the overall flow of control between computer

programs in a system.

2. It also shows the relationships among

a) various programs.

b) subsystems.

c) Files or database.

3. It documents the architectural structure of the overall system.

4. Processes are grouped into programs and subsystems based on similarities such as

shared timing.

Access to store data.

Users.

5. It graphically describes the organization of the subsystems into automated andmanual components showing the data flow , flow of control and interactions with

permanent data stores.

6. It is also used to describe systems that perform batch processing.


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7. In system flow chart, the individual data stores have been converted into database files.

Symbols Used


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Structured Chart

It is used to create a top-down decomposition of the functions to be performed by a

given program in a new system.

It always provides hierarchical organization of program functions.

It shows relationship between the modules of a computer program.

In structured chart level , we are not concerned with what is happening inside the

module.

The module at the very top of the tree is the boss module.

Order of module call will be always from left to Right.

structured chart maintains the strict hierarchy in the calling structure. Lower level

modules NEVER Calls Higher level modules.

The curved arrow immediately below the higher level module indicates a looping of the

modules to be called.


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Symbols Used in Structured Chart.

MODULE

COMMON SUB-ROUTINE

MODULE

CONTROL FLAG

DATA COUPLE


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DEVELOPING STRUCTURED CHART

There are two methods to design and develop structure chart.1. Transaction Analysis.

The development of a structured chart based on a DFD that describes the

processing for several types of transaction.

System flow chart and event table are use to develop the top level of the tree.

It is a process of identifying each separate transaction that must be supported bythe program and constructing a branch for each one.

2. Transform Analysis.

The development of a structure chart based on a DFD that describes the input

process, output process, Dataflow. It uses DFD fragments to develop sub trees, one for each event in a program.

Each sub-tree root module corresponds to the first level branch of the main

program structure chart.

It is based on the idea that computer program transforms input data into output

information.


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General form a structure chart developed with transform analysis is input-process-output.

Following Steps are followed to create Structure charts:

1. Determine the primary information flow.

2. Find the process that represents the most fundamental change from an input stream to

an output stream.

The output data stream is called the efferent data flow and central process is called

central transform.

3. Redraw the data flow diagram according to the DFD rules omitting non primary data.4. Generate first draft structure chart, based on the redrawn data flow, with calling

hierarchy and the required data couples.

5. Add other modules as necessary.

6. Add other required inter module relationships such as looping and decisions using

Structured English or Decision Tables.

7. Make the final requirement to the structure chart based on the quality controlconcepts.


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Integrity Control.

Integrity control mechanism and procedure that are built into the system to safeguard

both the system and the information contained within it.

Design of the interface must carefully consider mechanism to protect the system

integrity.

Objectives:

To Ensure that only appropriate and correct Business Transaction occurs.

To Ensure that the transaction are recorded and processed correctly.

i.e. to check for bugs, data entry errors and fraudulent processes.

To protect and safeguard the assets(including information) of the organization against

computer crash and Catastrophes.


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Managing User Access.

Most Common Technique for managing user access to information System is a user

identifier(User ID) and Passwords.

Two Techniques are used to defined Passwords:

1. Computer Generated.

2. User Defined. Some Syntax is always kept on passwords.

The security system should be organized so that all resources can be access using the

same unique identifier and password combination.

Another policy has to be designed to ensure ongoing security is that of changing

password periodically.

A final Security step is to make sure the system keeps a record or attempted logons.


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Input Integrity Controls:

They are used with all input mechanism.

As a system may need certain amount of information for valid entry but an input device

cannot ensure that all necessary fields have been entered, An additional level of

verification, which will call a control for necessary check for completeness.

Most Common control method to ensure correct input was to enter data twice. Thistechnique is called Keypunch Verify.

Common Control Technique that are used today are:

1. Field Combination Control.

E.g.: On a insurance policy, the application date must be prior to the date of policy.

2. Value Limit Control.

3. Completeness Control.4. Data Validation Control.


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Output Integrity Control

The purpose of output integrity controls is to ensure that output arrives at the properdestination and is correct ,accurate ,current and complete.

Especially important that reports with sanative information arrive at the proper

destination and they cannot be accessed by unauthorized persons.

Following items are controls that should be printed on reports:

1. Date and Time of report Printing.2. Date and Time of data on report.

3. Time period covered by report.

4. Beginning header with report identification and description.

5. Destination or routing information.

6. Pagination in the form of page-of-

7. Control Totals and Cross footings.8. End of Report Trailer

9. Report Version Number and Version Date.


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Design of input Systems

When designing inputs for the system. The system developer must perform four tasks:

1. Identify the devices and mechanism that will be used to enter input.

2. Identify all system inputs and develop a list with data content of each.

3. Determine what kinds of controls are necessary for each system input.

4. Design and prototype the electronic forms and other inputs.

Design of System outputs

When designing outputs for the system. The system developer must perform four tasks:

1. Determine the type of each output.2. Make a list of specific outputs required based on application design.

3. Specify any necessary controls to protect the information provided in the output.

4. Design and prototype the report layout.


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Type of output

1. External output.

2. Internal Output.

Type of Report

1. Detailed Report.

2. Summary Report.

3. Exception Report.

4. Executive Report.

5. Control Break Report.

6. Screen Output.

7. Drill Down.

8. Linking.

9. Graphical and Multimedia Presentation.


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Interface Design

Eight Golden Rules:

1. Strive for Consistency.

2. Enable frequent user to use Shortcuts.

3. Offer informative feedback.

4. Design dialogs to yield closure.

5. Offer Simple Error Handling.

6. Permit Easy Reversal of action.

7. Support internal locus of control.

8. Reduce short term memory load.


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END OF UNIT THREE


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OPERATING SYSTEMUNIT THREE


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SYLLABUS

MEMORY MANAGEMENT.

FILE MANAGEMENT.

I/O MANAGEMENT.

DISK MANAGEMENT.

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MEMORY MANAGEMENT

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Memory is central to the operation of a modern computer system.

Memory consists of a large array of words or bytes, each with its

own address.

The CPU fetches instructions from according to the value of the

program counter.

These instructions may cause additional loading from and storing

to specific memory addresses. A typical instruction-execution cycle, for example,

1. first fetches an instruction from memory.

2. The instruction is then decoded and may cause operands to be

fetched from memory.

3. After the instruction has been executed on the operands, resultsmay be stored back in the memory.

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What is Address Binding andexplain Compile, Loadand Execution Time ?

Reloadable Address.

Symbolic Address.

A user program may go through several steps before being executed. Addresses may be

represented in different ways during these. Addresses in the source program are generally

symbolic.

A compiler will typically bind these symbolic addresses to relocatable addresses and thelinkage loader will convert the relocatable addresses to absolute addresses.

Each binding is a mapping from one address space to another.

The binding can be done in the following ways:

Compile Time:If the address of the process is known at the compile time i.e. where the

process will stored in the memory, then the absolute code can be generated.Load Time: If the address is not known at the compile time then the compiler must

generate the relocatable code. In this case, final binding is delayed until load time.

Execution Time: If the process can be moved during its execution from one memory

segment to another, then binding must be delayed until run time.

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What is Logicaland PhysicalAddress Space?

An address generated by the CPU is commonly referred to as a logical address The address loaded in the memory address register of the memory is referred as physical

address.

What is dynamicloading ?

With dynamic loading, a routine is not loaded until it is called. All routines are kept on disk

in a relocatable load format.

The main program is loaded into memory and is executed.

When a routine needs to call another routine, the calling routine first checks to see

whether the other routine has been loaded.

If not, the relocatable linking loader is called to load the desired routine into memory and

then the control is passed to the newly loaded routine.

Advantage: 1) An unused routine is never loaded.

2) It does not require special support from the OS.3/16/2011 24


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Explain dynamiclinking and sharing oflibraries?

Some OS supports static linking, in which system language libraries are treated like any

other object module and are combined by the loader into the binary program image.The concept of dynamic linking is similar to that of dynamic loading, where linking is

postponed until execution time.

With dynamic linking, a stub is included in the image for each library routine reference.

When the stub is executed, it checks to see whether the needed routine is already in

memory. If not, the program loads the routine in the memory.

The stub replaces itself with the address of the routine and executes the routine.Using this scheme, all the processes that use a language, library execute only one copy of

the library code.

This feature can be extended to library updates, in which the program references the new

version of the library automatically.

Without dynamic linking, all the programs would need to be relinked to gain access to the

new library.

DISADVANTAGE:

Thus, only programs that are compiled with the new library version are affected by the

incompatible changes incorporated in it.

Other programs linked before the new library was installed will continue using the older

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Writea shot note on swapping?

A process must be in the memory to be executed.

A process however, can be swapped temporarily out of memory to

a backing store and then brought in the memory for continued

execution.

A variant of this swapping policy is used for priority-based

scheduling algorithms.This variant of swapping is sometimes called roll out,roll in.

Process that is swapped out will be swapped back into the same

memory space. This restriction is dictated by address binding.

If binding is done at assembly or load time, then the process

cannot be easily moved to a different location.

If execution-time binding is being used, however, then a process

can be swapped into a different memory space, because the

physical addresses are computed during execution time.

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Explain contiguous memoryallocation methodand its strategies

The memory is divided into two partitions: one for the resident OS and one for the user

processes.

The OS is placed either in the low or high memory.

The major factor affecting this decision is the location of the interrupt vector.

Since the interrupt vector is often in low memory, programmers usually place the OS in the

low memory as well. Simplest method is to divide the memory into several fixed partitions. Each partition may

contain exactly one process. Thus, degree of multiprogramming is bound by the number of

partition.

When process terminates, the partition becomes available for another process.

In fixed partition scheme, the OS keeps a table indicating which parts of memory are

available & which are occupied.Initially all memory is available for user processes & is considered as one large block of

available memory, a hole.

When a process arrives and needs memory, we search for a hole enough for this process

and used as much needed.

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The Strategies

1. First Fit: Allocate first hole that is large enough.2. Best Fit: Allocate smallest hole that is large enough.

3. Worst Fit: Allocate the largest hole.

* Fragmentation:

Both first and best fit suffer from external fragmentation.

As processes are loaded & removed from the memory the free space is broken intolittle pieces.

External fragmentation exists when there is enough total memory space to satisfy a

request but spaces are not contiguous.

This fragmentation problem can be severe. i.e. we could have a block of free spaces

between every two processes.

Statistics analysis of first bit, for instance, reveals that, given N allocated blocks,

another 0.5N blocks will be lost to fragmentation. i.e. one-third of memory is

wasted. This property is known as the 50-percent rule. It can be external or internal.

Solution: Compaction

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What is paging

Paging avoids the considerable problem of fitting memory chunks of varying sizes onto thebacking store.

The basic method for implementing paging involves breaking physical memory into fixed-

sized blocks called frames and breaking logical memory into blocks of the same size called

pages.

When a process is to be executed, its pages are loaded into available memory frames from

the backing store.The backing store is divided into fixed sized blocks that are of the same size as the memory

frames.

Every address generated by the CPU is divided into two parts: A page number (P) and a page

offset (D).

The page number is used as index into a page table.

The page table contains base address of each page in physical memory. This base address is combined with the page offset to define the physical memory address

that is sent to the memory unit.

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What is Segmentation and Explain segmentation withpaging?

Segmentation:

It is a memory management scheme that supports the user view of memory. i.e. a

logical address space is a collection of segments.

Each segment has a name and a length. Address specifies both the segments name &

the offset.

Logical address consists of a two:

Duple:

Segmentation withpaging:

Here, logical address space of a process is divided into partitions.

The first partition consist of up to 8 MB segments that are private to that process.

The second partition consist of up to 8 KB segment that are shared among all the

process.Info about the first partition is kept in the Local descriptor table (LDT); and Info about

the second partition is kept in the Global descriptor table (GDT).

Each entry in the LDT and GDT consist of an 8 byte segment descriptor with detailed

info about a partition segment, including the base location and the limit of that segment.

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VirtualMemoryManagement:

The common problem before programmers few years ago was how to fit large

programs into the small memory. The solution developed was to break

programs into small pieces called overlays.

Although the swapping was done by operating system, the work of creating

number of layers in a program was done by a programmer which was a time

consuming job.The virtual memory is a memory management technique which does the

splitting of a program into number of pieces as well as swapping.

The basic idea behind virtual memory is that the combine size of the program,

data and stack may exceed the amount of physical memory. The OS keeps only

those parts of the program in the memory which are required during executionand the rest on the disc.

Virtual memory is a memory management scheme that allows the execution of

process that may not be completely is main memory. In the other words, virtual

memory allows execution of partially loaded process. As a consequence user

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Advantages ofvirtual memory

1. The size of users program would no longer be considered by the available size of

physical memory.

2. Since each user utilizes less physical memory, more users can keep their programs

in the memory simultaneously which helps to improve CPU utilization and

throughput.

3. Since a process may be loaded into a space of arbitrary size, which in turn reduces

external fragmentation without the need to change the scheduled order of process

execution.

4. Moreover the amount of space in use by given process may be changing during its

memory residence. As a result the OS may speed up the execution of importantprocesses by allocating more physical memory.

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What is demand paging

Virtual memory is commonly implemented by demand paging. A demand-paging system is similar to a paging system with swapping.

When a process is to be swapped in, the pager guesses which pages will be used

before the process is swapped out again.

Instead of swapping in a whole process, the pager brings only those necessary

pages into memory. Thus, it avoids reading into memory pages into memory pagesthat will not be used anyway, decreasing the swap time and the amount of physical

memory needed.

With this scheme, The valid-invalid bit scheme is used for this purpose. When the

bit is set to valid, the associated page is both legaland in memory. If the bit is set

to invalid, the page either is not validor is validbut is currentlyon the disk.

The page-table entry for a page that is brought into the memory is set as usual, butthe page-table entry for a page that is not currently in memory is either simply

marked invalid or contains the address of the page on the disk.

Access to a page marked invalid causes a page-faulttrap.

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The procedure for handling this page fault is

1. If a process refers to a page which is not in the physical memory then an internal table

kept with PCB of that process is checked to verify whether a memory reference to a

page was valid or not.

2. If the memory reference to a page was valid, but the page is missing, then the process

to bring the referenced page into the physical memory starts.

3. Free memory location is identified to bring the missing page.

4. By reading the storage disk, the desired page is brought back into the free memory

location.

5. Once the page is in the physical memory, the internal table kept with the PCB of that

process and the PMT is updated to indicate that the page is now in memory.

6. Restart the instruction that was interrupted due to the missing page.

The hardware to support demand paging is

1. Page table: This table has the ability to mark an entry invalid through a valid-invalid bit.2. Secondary memory: This memory holds those pages that are not present in main

memory. The secondary memory is usually a high speed disk. It is known as the swap

device, and the section of disk used for this purpose is known as swap space.

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Explain pagereplacement

Page replacement takes the following approach.

1. If no frame is free, we find one that is not currently being used and free it.

2. We can now use the freed frame to hold the page for which the process faulted.

3. We modify the page-fault service routine to include page replacement.

Page ReplacementAlgorithm:

Find the location of the desired page on the disk.

Find a free frame:

If there is a free frame then use it.

If there is no free frame then use page replacement algorithm to select a

victim frame.

Write the victim frame to the disk; change the page and frame tables

accordingly.

Read the desired page into the new free frame; change the page and frame

tables.

Restart the user process.

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Whataredifferentpagereplacementalgorithms

1. FIFO Page Replacement:

2. Optimal Page Replacement

3. Least Recently Used Page Replacement:

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BeladyAnomaly

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END OF CHAPTER


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FILE MANAGEMENT

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Definition:

File is a collection of logically related data.

What are the different file attributes?

Name: The symbolic file name is the only info kept in human readable form.

Identifier: This unique tag, usually a number, identifies the file within the file system; it

is the non-human-readable name for the file. Type: This info is needed for systems that support different types of files.

Location: This info is a pointer to a device and to the location of the file on that device.

Size: The current size of the file and possibly the maximum allowed size are included in

this attribute.

Protection: Access-control info determines who can do reading, writing, executing, and

so on. Time, date, and user identification: This info may be kept for creation, last

modification, and last use. These data can be useful for protection, security, and usage

monitoring.


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Explain thedifferenttypes ofaccess methods?

SequentialAccess:

DirectAccess:

OtherAccess Methods:


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Explain thedifferentdirectory structures?

Single Level Directory:


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Two Level Directory:

Note: Tree Structure Directories:


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AcyclicGraph Directories:


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Explain the file system structure?

Application programs

LOGICAL FILE SYSTEM

FILE ORGANIZATION MODULE

BASIC FILE SYSTEM

I / O Control

DEVICES


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Writea short note in directory implementation?

Linear List

A linear list of directory entries requires a linear search to find a particular entry.

To create a new file, we must first search the directory to be sure that no existing file has

the same name. Then, we add a new entry at the end of the directory.

To delete a file, we search the directory for the named file, and then release the space to

it.

Disadvantage:

1. Linear search which is very slow.

Hash Table

Here, linear list stores the directory entries, but a hash data structure is also used.

The hash table takes a value computed from the file name and returns a pointer to the

file name in the linear list.So, the search time is decreased. Insertion and deletion are also fairly straightforward,

although some provision must be made for collisions.

Disadvantages:

1. Fixed size table and dependence of the hash function on that size.


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Explain thedifferenttypes ofallocation methods?

Contiguous AllocationIt requires each file to occupy a set of contiguous blocks on the disk.

Disk addresses a linear ordering on the disk.

Contiguous allocation of a file is defined by the disk address and

length of the first block.

Both sequential and direct accesses are supported by contiguousallocation.

Disadvantages:

1. Finding space f

or a new fi

le.2. External fragmentation


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LinkedAllocation

With linked allocation, each file is a linked list of disk blocks may be scattered

anywhere on the disk.

The directory contains a pointer to the first and last blocks of the file. To create a

new file, we simply create new entry in the directory.

With linked allocation, each directory entry has a pointer to the first block of the

file.

Advantage:

1. No external fragmentation

2. Any free block can used to satisfy a request.

3. Size of the files does not need to be declared when that file is created.

Disadvantage:

1. Effectively only for sequential access files.

2. Space required for pointers.

3. Reliability.


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Indexed Location

It brings all the pointers together into one location: the index block.

Each file has its own index block, which is an array of disk-block addresses.

The nth entry in the index block points to the nth block of the file.The directory contains the address of the index block.

To read the nth block we use the pointer in the nth index block entry to find and

read the desired block.

When file is created, all pointers in the index block are set to nil.

When nth block is first written, a block is obtained from free space manager and

its address is put in the nth index block entry.It supports direct access, without suffering from external fragmentation.

Disadvantage:

1. Wasted space.


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FREE SPACE MANAGEMENT


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BitVector:

Normally free space list is implemented as a bit map or bit vector.

Each block is represented by one bit.

If the block is free, the bit is one. If the block is allocated the bit is zero.

Advantage: Relative simplicity & Efficiency.

Linkedlist:

Here, we linked together all the free disk blocks, keeping a pointer to the first free block

in a special location on the disk and catching it in memory.

This first block contains a pointer to the next free disk block.

Disadvantage: We must read each block (for traversing the list) which requires substantialI/O.

Grouping:

To store the address of n free blocks in the first free block.

The first n-1 of these blocks are actually free.

The last block contains the addresses of another n free blocks.

Counting:

Rather than address we can keep address of first free block and number (n) of free

contiguous blocks that follows the first block.


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END OF CHAPTER


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DISK SCHEDULING


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Disk Scheduling

The seek time is the time for the disk arm to move the heads to the cylinder containingthe desired sector.

The rotationallatency is the additional time waiting for the disk to rotate the desired

sector to the disk head.

The disk bandwidth is the total number of bytes transferred, divided by the total time

between the first request for service and the completion of the last transfer.

Scheduling Techniques:

1. FCFS.

2. SSTF.

3. SCAN.

4. C-SCAN.


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Let us Consider disk queue with requests for I/O to blocks on cylinder.

98,183,37,122,14,124,65,67 and disk head is at 53.

1. First Come First Served.53 ,98,183,37,122,14,124,65,67

Total : 640 Cylinders.

2. Shortest Seek Time First

53,65,67,37,14,98,122,124,183Total : 236 Cylinder.

3. SCAN Algorithm

Assuming disk arm is heading towards zero.

53,37,14,65,67,98,122,124,183.

4. C-SCAN Algo

This is a special case of SCAN Algorithm.


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CPU SCHEDULING


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Scheduling Criteria

CPU utilization keep the CPU as busy as possible

1. Throughput # of processes that complete their execution per

time unit2. Turnaround time amount of time to execute a particular

process

3. Waiting time amount of time a process has been waiting in

the ready queue

4. Response time amount of time it takes from when a requestwas submitted until the first response is produced, not output

(for time-sharing environment)


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First Come First Served

Process Burst Time

P1

24

P2 3

P3

3

Suppose that the processes arrive in the order: P1 , P2 , P3The Gantt Chart for the schedule is:

Waiting time for P1

= 0; P2 = 24; P3= 27

Average waiting time: (0 + 24 + 27)/3 = 17

P1 P2 P3

24 27 300


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Shortest Job First Scheduling Algo

Associate with each process the length of its next CPU burst. Use these lengths to schedule the process with the shortest time.

Two schemes:

1. Non-preemptive once CPU given to the process it cannot be

preempted until completes its CPU burst.2. preemptive if a new process arrives with CPU burst length

less than remaining time of current executing process,

preempt. This scheme is know as the Shortest-Remaining-

Time-First (SRTF).

Note: SJF is optimal gives minimum average waiting time for a

given set of processes.


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Example of Non-Preemptive SJF

Process Arrival Time Burst TimeP1

0.0 7

P2 2.0 4

P3

4.0 1

P4

5.0 4

SJF (non-preemptive)

Average waiting time = (0 + 6 + 3 + 7)/4 =4

P1 P3 P2

73 160

P4

8 12


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Process Arrival Time Burst TimeP1

0.0 7

P2 2.0 4

P3

4.0 1

P4

5.0 4

SJF (preemptive)

Average waiting time = (9 + 1 + 0 +2)/4 = 3

P1 P3P2

42 110

P4

5 7

P2 P1

16

Example of Preemptive SJF


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Round Robin Algorithm

Each process gets a small unit of CPU time (time quantum),

usually 10-100 milliseconds.

After this time has elapsed, the process is preempted and added

to the end of the ready queue.If there are n processes in the ready queue and the time quantum

is q, then each process gets 1/n of the CPU time in chunks of at

most q time units at once.

No process waits more than (n-1)q time units.


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Process Burst Time

P1

53

P2 17

P3

68

P4 24The Gantt chart is:

Typically, higher average turnaround than SJF, but better response.

P1 P2 P3 P4 P1 P3 P4 P1 P3 P3

0 20 37 57 77 97 117 121 134 154 162

Example of RR with Time Quantum = 20


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Multi Level Queue Scheduling


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Assignment:

01.

02.

Note: Assume quantum = 1 unit for RR Algorithm

PROCESS ARRIVAL TIME BURST TIME

P1 0.0 8P2 0.4 4

P3 1.0 1

PROCESS BURST TIME PRIORITY

P1 10 3

P2 1 1

P3 2 3P4 1 4

P5 5 2


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END OF OPERATING SYSTEM


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JAVA SCRIPT


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What is the Document ObjectModel?

The Document Object Model is a platform- and language-neutral interface that will

allow programs and scripts to dynamically access and update the content, structure

and style of documents. The document can be further processed and the results of thatprocessing can be incorporated back into the presented page.


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Window Object

1. The Window object is the top level object in theJavaScript hierarchy.

2. The Window object represents a browser window.

3. A Window object is created automatically with every

instance of a or tag.


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Window ObjectMethods

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Method Description


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Method Description

alert() Displays an alert box with a message and an OK button

blur() Removes focus from the current window

clearInterval() Cancels a timeout set with setInterval()

clearTimeout() Cancels a timeout set with setTimeout()close() Closes the current window

confirm() Displays a dialog box with a message and an OK and a

Cancel button

createPopup() Creates a pop-up window

focus() Sets focus to the current window

moveBy() Moves a window relative to its current position

moveTo() Moves a window to the specified position

open() Opens a new browser window

print() Prints the contents of the current window

prompt() Displays a dialog box that prompts the user for input

resizeBy() Resizes a window by the specified pixels

resizeTo() Resizes a window to the specified width and height

scrollBy() Scrolls the content by the specified number of pixels

scrollTo() Scrolls the content to the specified coordinates

setInterval() Evaluates an expression at specified intervals

setTimeout() Evaluates an expression after a specified number of

milliseconds


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Window Object Properties

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Property Description


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Closed Returns whether or not a window has been closed

defaultStatus Sets or returns the default text in the statusbar of the window

Length Sets or returns the number of frames in the window

Name Sets or returns the name of the window

opener Returns a reference to the window that created the window

outerHeight Sets or returns the outer height of a window

outerWidth Sets or returns the outer width of a window

pageXOffset Sets or returns the X position of the current page in relation to the

upper left corner of a window's display area

pageYOffset Sets or returns the Y position of the current page in relation to the

upper left corner of a window's display area

Parent Returns the parent window

Scrollbars Sets whether or not the scrollbars should be visible

Self Returns a reference to the current window

Status Sets the text in the statusbar of a window

Statusbar Sets whether or not the browser's statusbar should be visible

Toolbar Sets whether or not the browser's tool bar is visible or not


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History Object

The History object is actually a JavaScript object, not an HTML DOM object.

The History object is automatically created by the JavaScript runtime engine and consists

of an array of URLs. These URLs are the URLs the user has visited within a browserwindow.

The History object is part of the Window object and is accessed through the

window.history property.


Length Returns the number of elements in the history list

Method Description

back() Loads the previous URL in the history list

forward()L

oads the next URL

in the history listgo() Loads a specific page in the history list


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EVENTS

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i f


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Properties of Event:


Current Target The node at which the event is beingcurrently processed

Target The node on which the event occurred.

Event Phase A number specifying the phase of the event

1. CAPTURING_PHASE

2. AT_TARGET

3. BUBBLING_PHASE

Time Stamp A date object that specifies when the event

occurred.

Bubbles A Boolean that specifies whether this event

bubbles up the document tree.

Cancelable A Boolean that specifies whether the event

has a default action associated with itthat can be cancelled with the

prevent_default() method.


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INTERNET EXPLORER EVENT MODEL

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IE Event Object Description

Type A string that specifies the type of event

that had occurred.

srcElement The document element on which the

event occurred

Button An integer that specifies the mouse

button that was pressed.

For multiple buttons we add up the

values.

Client X , Client Y These integers specify the mouse

coordinates at the time of the event,

relative to the upper left corner.

Integer Meaning

1 Left button

2 Right button

4 Middle button

CONTD


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CONTD

IE Event Object Description

offsetX, offsetY These integers specify the position of the

mouse pointer source element.

Altkey, ctrlkey, shiftkey These Boolean values specifies whether

these keys were held down when the event

occur.

Key Code This integer specifies the key code for key

down , key up events and the unicode

character code for keypress events.


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A SCRIPT

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