Question

Briefly discuss what block allocation is and how it is organized. What is partitioning?

Answer 1

background
block are allocated a per the need of process/objects,if memory blocks are allocated without any proper plan/policy then unplanned allocation may produces memory holes(leftover memory after allocation).if these hole can not be use for further allocations,it is a wastage of memory(called fragmentation)
there can be two types of memory fragmentation
1)internal fragmentation
2)external fragmentation

Ans
To produce the output, process/data/programs need some memory.
memory blocks are allocated according to some policies.
each block allocation policy has its advantages and disadvantages.
There are 3 policies to allocate the blocks.
1.First fit
2.Best fit
3.Worst fit

1. First fit:-it is a memory allocation scheme. according to this scheme, entire memory is scanned from Beginning to end until the first free space if found, but this space should be large enough to accommodate the required data/process.
advantages
a)Fast
b)simple algorithm
c)there is no need to perform sorting
disadvantages
a)this scheme does not provide the optimize allocation.
b)the intention of this scheme is just to allocate first available space( which can accommodate the required object/data/process) which may result in wastage of memory.
this scheme does not care about the left over memory after allocation.

2.Best Fit:-As the name suggested to this scheme, this memory block allocation scheme searches the entire list of free blocks and allocates the smallest block( which can accommodate the required object/process).
advantages
memory utilization is far better than first fit
disadvantage
a)slow
b)since, this scheme allocates smallest block which may produce very small holes(may not be allocated due very small in size)

3.worst fit:- the basic idea behind this allocation scheme is to allocate the largest block to store the object/process to have large leftover(hole, these large holes can be use for further allocations)
advantage
it reduces the chances of production of small holes(very small holes can not be allocated).
disadvantage
if there is a request for a large block.then this scheme may not full fill the demand, because large hole has been already used.

Partitioning:

A hard disk is logically divided into number of parts. each part is treated as a saperate unit by the operating system.partitioning reduces the usable space on the hard disk, because some more control information needs to be stored to manage these partitions(c:\,d:\,e: drives)
partitioning makes searching easy and fast.
advantage of partitioning can be well explained with the hep of following example.
a)consider if a city is not divide on the basis of zip numbers, then it would be difficult to spot the locations
bin the city.
b)searching a person in city(if city is not divided into areas) is difficult.