GATE CSE 2003 | Question: 25, ISRO2009-12
in Operating System retagged by
35 votes

Using a larger block size in a fixed block size file system leads to

  1. better disk throughput but poorer disk space utilization
  2. better disk throughput and better disk space utilization
  3. poorer disk throughput but better disk space utilization
  4. poorer disk throughput and poorer disk space utilization
in Operating System retagged by

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4 Answers

64 votes
Best answer

Answer is (A). Larger block size means less number of blocks to fetch and hence better throughput. But larger block size also means space is wasted when only small size is required.

edited by


not getting

plzz explain briefly
if i have fixed block size file sys..let-10kb

my file size is 9kb..much large or take 12kb

nw througput-no. of processes per unit time. file of size 9kb or 12 kb most of the time is utilize.. but for that lot of memory is wasted.
Disk throughout is asked, the explanation says processor throughput will be more.

I guess if disk throughput measured in bits/sec. Since less block will mean less overhead (block metadata etc), a higher bits/sec throughput can be expected. Since fewer bits of metadata/headers, efficiency will be higher and so will effective throughput.
Can we relate large block size with spatial locality ?
edited by
That is already assumed, large block size, fewer page faults because of spatial locality :)
A block in a file will be equal to a sector in disk...So how will we relate the larger block size to a sector on disk?
Disk throughput is also depends on Size of System Bus.

@vaishali jhalani

A block in a file is equal to the block in disk.

one block in disk consists of one or more number of sectors.



Larger block size how it helps to get better DISK throughput ..

Throughput = data/sec .... larger the data block, throughput will increase and will require less block access.
But it also adds to internal fragmentation if file size not equal to block size as mentioned by arjun sir.
31 votes

ans is a 

If block size is large then seek time is less (fewer blocks to seek) and disk performance is improved, but remember larger block size also causes waste of disk space.

–5 votes

Using larger block size makes disk utilization poorer as more space would be wasted for small data in a block. It may make throughput poor as the number of blocks would decrease.
–6 votes
The answer should be C na ?

Due to larger block size

the disk would have better space utilization as compared to largest one . Because if the largest block size is taken then small data would have great amount of internal Fragmentation as compared to larger one

And due to larger block size ,nno of thought put will be poorer only


Answer is A. Larger block size means less number of blocks to fetch and hence better throughput. But larger block size also means space is wasted when only small size is required.


SIR, please tell where I am wrong:

Let any disk then if block size is big the no. of blocks in that disk will be less but space will be utilized. If we have small small blocks in same space then there can be chance of more gaps and so poor space utilization as size of file is fixed. Throughput is related to no. of blocks access per unit time. so, is it like time will be more to access larger blocks???


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