The "7.8 Mb" problem

There are two types of partitions: Primary partitions and Extended partitions. One can create only four partitions on every single hard disk drive. Please note that also there can be only one Extended partition on each hard disk drive. So there are only eight partition configurations of a hard disk drive:

1) One primary partition
2) Two primary partitions
3) Three primary partitions
4) Four primary partitions
5) One primary partition + one extended partition
6) Two primary partitions + one extended partition
7) Three primary partitions + one extended partition
8) One extended partition

Further more, Primary partition can be set Active. There can be only one Primary Active partition on each hard disk drive.

Every Extended partition consists of several (one or more) logical disks.

The "7.8 Mb" problem:

1) The 7.8 Mb of unallocated space is in the end of a hard disk drive (it is created in order to allow Windows to convert basic disks into dynamic ones). In this case this unallocated space can be merged into an adjacent Primary partition / Logical disk in Extended partition.

2) The 7.8 Mb of unallocated space is in the beginning of a hard disk drive. In this case this space can be merged only into an adjacent Primary partition. The thing is that an Extended partition can't start from the very beginning of a hard disk drive. So if you try to merge this unallocated space into a Logical disk in Extended partition - this operation will not succeed.