But this interface was incompatible with the previous one, and old operating systems, such as DOS, which used old BIOS interfaces, couldn't exceed 8 GBytes. Practically all modern systems do not now use the BIOS, they are utilizing their own drivers for working with discs. But note that before using their own drivers the systems first have to load them. Now we will look at how operating systems are placed on hard discs. For this purpose a disc address space of blocks is divided into partitions.
Partitions are similar to a whole disc in the fact that they consist of adjacent block.
So, for description of a partition it is necessary to specify the beginning of a partition and its length in blocks. A hard disc can contain 4 primary partitions. In the beginning of this sector there is a boot code which reads the partition table and defines an active partition. And then the sequence of operations repeats. I.e. it loads a boot sector of this partition according to the same address and passes over the control.