In the following cases the sequential allocation method is not acceptable:

1. Unpredictable Storage Requirements:

In such type of cases it is not possible to find out the exact amount of memory required. The exact amount of memory required depends upon the data that will be entered by the user. This requirement can not be known in advance and can only be assumed. If we assume less than the actual requirement then the program will be useless for the user, like we have assumed that the maximum numbers a user can enter is 50 but user wants to enter 100 numbers. In this case user does not have enough space available so the program will not work according to user requirements. If we assume more than the actual requirement then there will be wastage of memory, like we have assumed that the maximum numbers a user can enter is 100 but user wants to enter 10 numbers at the most. In this case there will be wastage of memory space allocated to 90 numbers.

As in case of sequential allocation, we have to tell in advance how much memory is to be reserved and the memory once reserved can not be increased or reduced, so this method is not useful in such type of cases.

2. Extensive Manipulation of the Stored Data:

In these cases, programs typically require that the operations of insertion and deletion are to be performed frequently on the data. Such operation can not be performed easily in case of sequential allocation and are very time consuming. So in such cases sequential allocation method is not acceptable.

In such cases linked allocation method is used in place of sequential allocation.