Operating System - Allocation Methods

1. ALLOCATIONMETHOD
Subject: Operating System
P. Indhuja MCA., M. Phil.,
Department of BCA
E.M.G. Yadava Womens College

2. DEFINITION:
FILE ALLOCATION METHODS ARE DIFFERENT WAYS BY WHICH THE OPERATING
SYSTEM STORES INFORMATION IN MEMORY BLOCKS, THUS ALLOWING THE HARD DRIVE
TO BE UTILIZED EFFECTIVELY AND THE FILE TO BE ACCESSED.
MEMORY BLOCK:
RAM, WHERE INPUT DATA IS STORED BEFORE AND AFTER PROCESSING
IN THE CPU.

3. ALLOCATION METHODS TYPES:
 Contiguous Allocation
 Linked Allocation
 Indexed Allocation

4. CONTIGUOUS ALLOCATION:
 Contiguous Allocation is basically a method in which a single
contiguous.
 Section/part of memory is allocated to a process
or file needing it.
 Its can seen as problem in a particular application which presented
In dynamic storage allocation.
 An algorithms also suffer in external fragmentation.

5. Example CMA:

6. LINKED ALLOCATION:
 The definition of linked allocation, is each file is a linked
list of disk blocks.
 Each individual file is considered to be a linked list of
file blocks.
 A linked list is a data structure that is based on dynamic
memory allocation.
 There is no external fragmentation because blocks can be
allocated random order with the help of pointers.

7. Example

8. HINT:
 Each file is a linked list of blocks
 No external fragmentation
 Effective for sequential access
 Problematic for direct access.

9. INDEXED ALLOCATION:
 The indexed allocation, saves all disc pointers in one of the blocks
known as an indexed block.
 It does not connect file data but, it contain to link all disc blocks.
 Mapping from logical to physical in a file of maximum size of 256k
words and blocks size of 512 words.
 It can be read and write in a single disk operation.
 It is used to write in the documentation in disk.

10. Example:

11. Type:
 Linked scheme
 Multi level Index
 Combined scheme

12. Example:

13. PERFORMANCE:
o Two criteria:
a) Storage utilization efficiency,
b) Data block access time.
CA: Good for known size file.
LA: Good for storage utilization.
IDA:Access time depends on index structure,file,size,block position.

14. Conclusion:
These File Allocation Methods in the OS determine how files are stored on the disk
drive, which has an effect on file access time in the computer. Their primary goal is to
maximize the use of available space and minimize fragmentation, which can impede
file access and reduce overall system performance.