Q: how to create dual boot disk with ubuntu 32-bit and 64-bit
 

Assume I have one new (empty) 1TB disk drive and want to create a dual-boot linux system that boots <32-bit ubuntu 8.04.1> or <64-bit ubuntu 8.04.1>. How do I go about that?

As a separate but related question, is linux in general (as well as ubuntu in particular) organized so all the files for both 32-bit and 64-bit linux can coexist on the same filesystem (and same partitions)? Since we get 4 primary partitions, can they (or should they) be: "/boot", "/boot64", "/" and "swap"? Or do the two OS even need separate boot partitions?

To extend the question, I have two more 250GB disk drives and might want to put 32-bit and 64-bit fedora9 on those and make the system quad-boot. Is that practical too? And how would that best be partitioned? I would prefer those two drives be able to boot independently (meaning, with all the other disk drives unplugged from the motherboard).

In case it matters, all the disk drives are SATAII.

The same way you would create a dualboot system between any other two distros. I seriously doubt 32bit Ubuntu and 64bit Ubuntu, could share home, which it sounds like you're asking. The two distros might be able to share swap space, but I really don't know on that one. Here's how I would do it.

Partitions 1 and 2 32bit-- 4gig Swap, 75gig /
Partitions 3 64bit-- 75gig /

Rest of the available drive, setup as /files or whatever name you want, format as Fat32(not sure how NTFS support is in 64bit, but it might work also).. and any files you want to share between the two.(MP3s, movies, pics, whatever). A bit different, but thats how I have my 1 dual boot machine set up...

Partition 1--XP Home--25gigs
Partition 2 and 3--- Swap(4gigs) and Ubuntu / --60gigs
Partition 4--- Fat32---220gigs

IGF

IndyGunFreak has the solution, I personally allow about 20 Gig for home on my distros and create a fat 32 for data. I try and keep my os's clean and any data gets put into the data partition. This allows any distro to mount and read/write the partition without any add ons. The main problem with a large data partition is keeping your files strait, I figured an index system for mine.

Why? It wouldn't really be helpful for, say, benchmarking and there isn't that much difference between the 32 and 64 bit versions that I'd want to be booting both continuously (maybe try both, then decide), so I'm not sure I see the objective. Well, not a worthwhile one, anyway.

In my case, I have developed a 3D simulation/graphics/game engine designed to be compiled in 32-bit and 64-bit mode to run on 32-bit and 64-bit Linux. When compiled as a 64-bit program, all [1/2/4+] CPU cores have twice as many [SIMD] registers, which makes the core matrix and vector math/transformation routines significantly more efficient (shorter and faster). Therefore, to test both 32-bit and 64-bit versions of the program, I think it is best to have both versions of Linux to test on.

In theory, I suspect it is sufficient to develop and test entirely on 64-bit Linux, since the tools will still compile 32-bit versions, which should run okay as 32-bit programs on 64-bit Linux. However, the nvidia/ati video drivers are different, which introduces a slight chance "things will work differently" on 32-bit and 64-bit Linux. And honestly, I am not even sure the 32-bit compilations of my program would run on 64-bit Linux --- I'm not sure how my 32-bit program can properly link to the various nvidia 64-bit drivers. I think it is supposed to work, but I don't quite understand how it can, now that I think about it.

Anyway, I know that most 32-bit Linux programs are supposed to run on 64-bit Linux, and for most normal computer users, I agree a single 64-bit Linux should handle just about every 32-bit and 64-bit application. But I'm a software developer and want to make sure my applications run for everyone on every Linux.

But still, it could be I'm missing something. Obviously I am not entirely clear about how every aspect of 32-bit / 64-bit compatibility works. Please feel free to enlighten me - or point me to a book, article, webpage, reference that explains.