First Fit :

In the first fit approach is to allocate the first free partition or hole large enough which can accommodate the process. It finishes after finding the first suitable free partition.

Advantage : Fastest algorithm because it searches as little as possible.

Disadvantage : The remaining unused memory areas left after allocation become waste if it is too smaller. Thus request for larger memory requirements cannot be accomplished.

Best Fit :

The best fit deals with allocating the smallest free partition which meets the requirement of the requesting process. This algorithm first searches the entire list of free partitions and considers the smallest hole that is adequate. It then tries to find a hole which is close to the actual process size needed.

Advantage : Memory utilisation is much better than first fit as it searches the smallest free partition first available.

Disadvantage : It is slower and may even tend to fill up memory with tiny useless holes.

Worst fit :

In worst fit approach is to locate the largest available free portion so that the portion left will be big enough to be useful. It is the reverse of best fit.

Advantage : Reduces the rate of production of small gaps.

Disadvantage : If a process requiring larger memory arrives at a later stage then it cannot be accommodated as the largest hole is already split and occupied.