The document summarizes Anand M. Khandare's seminar on implementing a file structure in an operating system. It discusses various topics related to file systems including file system structure, allocation methods like contiguous, linked and indexed allocation, free space management techniques, disk structure, disk scheduling algorithms, disk management, RAID concepts, and I/O systems. It provides details on each topic with examples and diagrams.

1. SEMINAR ON
OPERATING SYSTEM
Topic : Implementing a
file Structure
By..
Anand M. Khandare
M.Sc. - I

2. 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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3. 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)
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 File control block – storage structure consisting of
information about a file
 Device driver controls the physical device
 File system organized into layers 3

4. LAYERED FILE SYSTEM
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5. ALLOCATION METHODS
 Why Allocation Method ?
Utilization Of Disk Space Effectively
To Increase the Accession Speed
 Major Method of Allocation:
Contiguous
Linked
Indexes
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6. Contiguous Allocation
 A Set Of Contiguous Block
 Example : IMB VM/CMS
 Access :
 Sequential
 Direct
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7. CONTIGUOUS ALLOCATION OF DISK
SPACE
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8. PROBLEMS
 Finding Space For new File?
 Chosen To manage free space determine ,
how this task complete ?
Solutions : First fit And Best Fit
 External Fragmentation
Solution: Floppy Disk
 Time consuming Operation
solution : Preallocation , Modified Contiguous
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Allocation Scheme 8

9. 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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10. LINKED ALLOCATION
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11. 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 block
number in each block
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12. 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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13. EXAMPLE OF INDEXED
ALLOCATION
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14. PROBLEMS
 In the case if file if the file is small then you are
create one index?
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15. REUSE
The concept of
Reusing in
Computer
Science
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16. 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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17. BIT VECTOR OR BIT MAP
1 And 0
traversing bit by bit
0 1 2 n-1
…
bit[i] =

1 Þ block[i] free
0 Þ block[i] occupied
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18. 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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19. EXAMPLE
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20. DISK STRUCTURE
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21. 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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22. 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
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 FCFS Scheduling
 SSTF Scheduling
 SCAN Scheduling
 C- SCAN Scheduling
 LOOK 22

23. FCFS SCHEDULING
 First Come First Serve
 Simple to manipulate
 Does not provide fastest service
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24. 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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25. 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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26. C- SCAN SCHEDULING
 Provides a more uniform wait time than SCAN
 Reverse of SCAN
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27. LOOK SCHEDULING
 Combination of SCAN and C- SCAN
 They look for request before continuing to move
in the given direction
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28. DISK MANAGEMENT
 Disk initialization
 Booting from Disk
 Bad Block Recovery
 Boot block
 Disk Formatting
 Low Level
 Physical/high level
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29. 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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30. DIAGRAMMATIC
REPRESENTATION :
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31. 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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32. 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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33. 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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34. I/O HARDWARE
 Storage Devices
 Transmission devices
 Human interface device
 Communicate via signal
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35. INTERRUPTS
 signal to the processor emitted by hardware or
software
 Hardware Interrupt
 Software Interrupt
 Interrupts Request Line
 Interrupts Handler
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36. 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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37. 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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38. KERNEL OF I/O SUB SYSTEM
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39. REFERENCES
 Wikipidia.com
 Operating System Principle
 by..
ABRAHAM SILBERSCHATZ
GREG GAGNE
PETERBAER GALVIN
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