Disk performance is critical for overall system performance as disks are much slower than other components. Two key techniques for improving disk performance are block caching and block read ahead. Block caching stores frequently accessed disk blocks in faster RAM. Block read ahead preemptively loads sequential blocks from disk into cache before they are requested. Example file systems discussed include CD-ROM (using ISO 9660), MS-DOS (using FAT16), and UNIX (using a hierarchical structure with everything treated as a file).

1. FILE SYSTEM PERFORMANCE
VIJAY YADAV
072/BCT/547

2. •Disk is the slowest part of computer.
•Disk is at least 100,000 times slower than RAM
and over 2 million times slower than CPU.
•So, when it comes to performance of PC ,disk
performance should be focused

3. Disk access time= seek time + latency(rotational)
time
SEEK TIME:- is the time it takes for the read-write head
to move over the appropriate track.
LATENCY:- is the time it takes for the disk to rotate the
correct sector under the read-write head.

5. Disk performance can be increased using
following concepts:-
•Block Cache
•Block Read Ahead

6. (A) Block Cache
• Cache is a collection of blocks
• First check whether the required block is in cache or
not.
• If it is, the read request can be satisfied without a disk
access.
• If the block is not in the cache, it is first read into the
cache, and then copied to wherever it is needed.

7. (B) Block Read Ahead
• Blocks are read into the cache before they are needed
to increase the hit rate.
• It is mainly used in sequential file access .
• But sequential and random access attributes can be
attached in file attribute to perform both access.

8. Example File Systems
•CD- ROM File System
•MS-DOS File System
•UNIX File System

9. (A) CD-ROM file system
• The ISO 9660 File System is the first CD-ROM file
system standard.
• Every CD-ROM have
•Starting 16 blocks used by manufacturer to provide
a bootstrap program to allow the computer to be
booted from the CD-ROM, or for some other
purpose.

10. • One block for primary volume descriptor, Which contains
• The system identifier (32 bytes), volume identifier (32
bytes), publisher identifier (128 bytes), and data
preparer identifier (128 bytes).
• Three file abstract, copyright notice, and bibliographic
information, respectively.
• Key numbers for logical block size (normally 2048, but
4096, 8192, and larger powers of two are allowed in
certain cases), the number of blocks on the CD-ROM,
and the creation and expiration dates of the CD-ROM.
• A directory entry for the root directory, telling where to
find it on the CD-ROM.

12. (B) MS DOS file system
• It is a 16-bit system based on a File Allocation Table, or
FAT16.
• The purpose of the file allocation table is to keep track
of where to find files on the disk.

13. • In MS-DOS, every DOS based partition has a letter: (A:
or B: or C:).
• Typically, the drive letters A: and B: are reserved for
floppy drives.
• We can most frequently find that the C: drive is the
'bootable partition’.
• Each drive has a root directory ('') so the root
directory on a given drive looks like this: C:

14. (C) UNIX file system
• Everything in Unix is considered to be a file, including
physical devices such as DVD-ROMs, USB devices, and
floppy drives.
• Unix uses a hierarchical file system structure, much
like an upside-down tree, with root (/) at the base of
the file system and all other directories spreading
from there.

15. A typical UNIX file system