Can someone help me find the documentation of the algorithm used to assign logical drive numbers for disk devices? When I say "drive numbers" I mean the "#" in /dev/hda#.


If someone wants to correct my terminology feel free; I am not sure what is correct for Unix/Linux.

I betcha if I don't say that it is not sequential someone will say I don't need documentation that it is just sequential from the first partition to the last on the physical drive. I know that hard drive partitions can be primary, extended and logical partitions or something like that. I did know all about them a few years ago but I need to refresh my memory. I can do that but the important thing is that it appears to me that linux does not assign the numbers strictly sequentially.

The reason I am asking is because I want to know how to relate Unix/Linux drive designations to Windows drive letters. The Unix algorithm is simpler since a drive's designation is independent of the other drives but I can figure out the Windows algorithm.

In Linux first hd is hda, second hdb and so on. Primary partitions are hda1, hda2,..., extended start from hda5. Partintions are numbered as they are created, so it may happen that hda7 will be before hda5.

Do you know where that is documented?

Do you know how it is determined when a partition is "created"? I do not recall a creation date for partitions. I think the volume serial number is a date but that is relatively new and the Unix drivers that determine drive numbers is older than volume serial numbers.

What you are saying about primary partitions being numbered 1 to 4 and extended partitions being numbered starting from 5 is interesting. You are probably correct about that and that probably helps a lot. I would like to find the documentation though to ensure I have all the important details.

Perhaps instead of writing a Windows program first I should write a Linux program to show partitions and their logical drive numbers. Then I would be more likely to get people to test it and check it's accuracy. I suppose I would need the documentation of the relevant device drivers, and that is a likely place for finding the documentation I am asking about. So I should find the documentation of the disk device drivers.

Visit www.linuxdoc.org. What will be interesting for you is: "Kernel 2.4 Internals", "The Linux Kernel" and "Linux Programmer's Guide". Also other files, of course.
From www.kernel.org you can take Linux kernel. It may be interesting to read it's documentation, which is included.