SEMINAR ON OPERATING SYSTEM

Topic : Implementing a file Structure

By..

Anand M. Khandare

M.Sc. - I

CONTENT :

File System Structure Allocation Methods Free Space Management Disk Structure Disk Scheduling Algorithm Disk Management RAID (concept) I/O System

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FILE SYSTEM STRUCTURE

File structure Logical storage unit Collection of related information

File system resides on secondary storage (disks) Provided user interface to storage, mapping logical to

physical Provides efficient and convenient access to disk by

allowing data to be stored, located retrieved easily Disk provides in-place rewrite and random access

I/O transfers performed in blocks of sectors (usually 512 bytes)

File control block – storage structure consisting of information about a file

Device driver controls the physical device File system organized into layers 3

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LAYERED FILE SYSTEM

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ALLOCATION METHODS

Why Allocation Method ? Utilization Of Disk Space

Effectively To Increase the Accession Speed

Major Method of Allocation:ContiguousLinked Indexes

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Contiguous Allocation

A Set Of Contiguous Block Example : IMB VM/CMS Access :

Sequential Direct

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CONTIGUOUS ALLOCATION OF DISK SPACE

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PROBLEMS

Finding Space For new File? Chosen To manage free space determine ,

how this task complete ?Solutions : First fit And Best Fit

External FragmentationSolution: Floppy Disk

Time consuming Operation solution : Preallocation , Modified Contiguous

Allocation Scheme8

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LINKED ALLOCATION

Solved All problems of Contiguous allocation Linked list of disk block Contains a Pointer. Block Size 512 bytes Initially Pointer is nil . No external Fragmentation

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LINKED ALLOCATION

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PROBLEMS

Used only for sequential Access file A pointer require a disk Space About 0.78% Solution:1. collections of block in clusters .2.FAT What happen when Pointer were lost or

damage? Solution: Sore the file name and relative

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INDEXED ALLOCATION METHODS

Fragmentation And Size declaration Problem in contiguous can`t solve with out FAT.

Bringing all pointers At ONE locations. Each file one Index block Support Direct access.

Linked scheme Multilevel index Combined Scheme

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EXAMPLE OF INDEXED ALLOCATION

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PROBLEMS

In the case if file if the file is small then you are create one index?

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REUSEThe concept of Reusing in Computer Science

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FREE-SPACE MANAGEMENT

Reuse the space Reuse is not physically possible. Free Space list Different way to Management

Bit Vector Linked list Grouping Counting

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BIT VECTOR OR BIT MAP

…

0 1 2 n-1

bit[i] = 1 block[i] free

0 block[i] occupied

1 And 0 traversing bit by bit

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LINKED FREE SPACE LIST ON DISK

Link together all the free disk , blocks , keeping pointer to first free block in special location on the disk And catching it in the memory

It is efficient as compare to bit vector In FAT method incorporates free block

accounting

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EXAMPLE

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DISK STRUCTURE

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DISK STRUCTURE

Large one dimensional array of logical block Logical block – Smallest unit of transfer (512 byte) CLV( Constant Linear Velocity)

CD-ROM DVD-ROM

CAV(Constant Angular Velocity) HDD

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DISK SCHEDULING

Why Disk Scheduling ? Use the hardware efficiently Fast access time Large disk Bandwidth“Bandwidth” is total no of byte

transferred ,divided by the total time between the first request for service and completion of the last transfer.

Way for Disk Scheduling FCFS Scheduling SSTF Scheduling SCAN Scheduling C- SCAN Scheduling LOOK

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FCFS SCHEDULING First Come First Serve Simple to manipulate Does not provide fastest service

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SSTF SCHEDULING Shortest Seek Time First Select the request with the minimum seek

time SSTF may cause starvation of some requests

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SCAN SCHEDULING Variant of SCAN design to provide It immediately returns beginning of the disk SCAN algorithm Sometimes called the elevator

algorithm

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C- SCAN SCHEDULING Provides a more uniform wait time than SCAN Reverse of SCAN

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LOOK SCHEDULING Combination of SCAN and C- SCAN They look for request before continuing to

move in the given direction

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DISK MANAGEMENT Disk initialization Booting from Disk Bad Block Recovery Boot block Disk Formatting

Low Level Physical/high level

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BOOT BLOCK

Contain The machine Code Loaded in RAM We can Select boot device Boot Start up in ROM A disk that has boot partition is called system

Disk/Boot Disk

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DIAGRAMMATIC REPRESENTATION :0

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SWAP-SPACE MANAGEMENT

“Swap-space” Virtual memory uses disk space as an extension of main memory

Moving Entire process Between disk And Main Memory

Modern operating system implementation Low Level Task Swap Space use Swap space Location

raw

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RAID

Redundant Array Of Inexpensive Disks Data storage virtualization technology Purposes of data redundancy or performance

improvement An error protection scheme

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I/O SYSTEMS

Main job of computer I/O Hardware I/O Services provided by the OS Control I/O operation and divices

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I/O HARDWARE

Storage Devices Transmission devices Human interface device Communicate via signal

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INTERRUPTS

signal to the processor emitted by hardware or software Hardware Interrupt Software Interrupt

Interrupts Request Line Interrupts Handler

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DMA

Direct memory access (DMA) is a feature of computerized systems that allows certain hardware subsystems to access main system memory independently of the central processing unit

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APPLICATION OF I/O INTERFACE

I/O is the communication between an information processing system (such as a computer) and the outside world, possibly a human or another information processing system. Inputs are the signals or data received by the system and outputs are the signals or data sent from it

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KERNEL OF I/O SUB SYSTEM

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REFERENCES

Wikipidia.com Operating System Principle

by..

ABRAHAM SILBERSCHATZ

GREG GAGNE

PETERBAER GALVIN

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