Removable Hard Disk Drive

Hi,

With respect to a "removable hard disk drive" what would B128, B96,
B64 and B32 stand for ??

The piece of code I am reading doing a convertion between A and B
where
A =
     unsigned long   num_Major;
     unsigned long   num_Minor;
     unsigned int    num_Disk;
     unsigned int    num_Dkc;  // Disk Controller
     unsigned int    num_Dport;
     unsigned int    num_Hba;
     unsigned int    num_Hport; // Host Port
     unsigned int    num_Bus;
     unsigned int    num_TId;
     unsigned int    num_Hlu;  // Host Logical Unit

B =
struct B
{
    unsigned int B128;
    unsigned int B96;
    unsigned int B64;
    unsigned int B32;
};

Would help if I could get some clue on what they stand for.

Thanks and Regards,
M Shetty