Question How many drive letters can you have on one hard drive?
Answer: There are 26 available drive letters. Two of these are pre-allocated to floppy drives leaving 24. If you don't have any other drives that need drive letters assigned then you ought to be able to partition a hard drive into one primary and 23 logical partitions and use all of the drive letters C - Z on one drive.
In practice the limit is likely to be much lower. The disappearance of floppy drives from computers has not changed the fact that the operating system still reserved two drive letters for their use. Most computers now have a DVD or BluRay drive for handling external media and so that will use op one of the available drive letters. Also many computers are now connected to networks where some drive letters are allocated to drives located on other computers on the network. There are also many storage devices that can be attached to one of the USB ports on the computer. These can vary from a small USB stick that only holds a few MegaBytes (although most now hold a few Gigabytes) through to external hard drives that can hold a few TeraBytes.
So if you had a DVD drive, perhaps five network drives, and keep a couple of drive letters spare for when you want to connect USB storage you would only be able to use 16 drive letters on your internal hard drive.
This article written by Stephen Chapman, Felgall Pty Ltd.