Actually, i dont know where you got the 7.8 GB limitation. As far as I know, there is a 2GB limitation per partition, not hard drive. The reason is simple. DOS supports a FAT16 file system. FAT16 has a maximum cluster size of 32KB. It also has a maximum number of allocation units of 65,536.
Think of an allocation unit as a box. DOS can only track 65,536 of these boxes per partition. Each partition can hold a maximum of 32K each.
So, just do the math...
65,536 x 32KB = 2,097,152 KB
2,097,152KB / 1024 = 2,048 MB
2,048 MB = 2 GB.
So, back to the hard drive. With the FDISK utility in DOS, you can create 2 partitions. One primary and one extended. In the primary partition, you can have one logical drive. in the extended partition, you can have up to 23 logical drives). Between the primary and secondary you can have 24 logical, 2GB maximum drives (Drive C-Z). Note that Drive A and B are reserved in DOS for floppy drives.
The most amazing thing is that I still remember this from more than a decade ago, but i have trouble remembering what I had for lunch yesterday. Go figure...
DOS uses logical drives that are 2 GB or less and within the 7.8 GB total disk space limit...i got this from a class about DOS ..i understand what u explain ..i just don't understand the 7.8 GB limitation ..may be this info is wrong !!!