Formatting HDD to be available in both MacOS9 and WinXP

Hi, TS. The short answer is that you can't do it.

OS 9 can only handle volumes up to 200GB in size, and there's no way to partition a larger drive to create separate cross-platform volumes on it. OS 9 can't read NTFS format, either: FAT32 is the only volume format compatible with both WinXP and OS 9. Setting up a drive with two FAT32 partitions smaller than 200GB will work on the PC, but the Mac won't understand the PC partition map, so neither volume will be recognized in OS 9. The essential problem is that Macs and PCs write partition maps very differently.

If the drive in question were smaller than 200GB, there'd be no problem: format it FAT32 and she'd be good to go.

A drive formatted as Mac OS Standard can't have OS X installed on it; OS X requires Mac OS Extended. Mac OS Extended makes far, far more efficient use of hard drive space than the much older Mac OS Standard format.

If you're saying Mac OS 9 is recognizing a single Mac OS Standard-formatted volume of 238GB, I don't understand that. If the drive were correctly formatted (as Mac OS Extended), Apple says that would be impossible:

http://docs.info.apple.com/article.html?artnum=86178

Note that the the article's title focuses primarily on a hardware limitation imposed by the internal ATA bus in some Macs (which is irrelevant to your question), and not on the volume size limitation imposed by OS 9 itself. But that volume size limitation is mentioned in it:

"If you plan to start the partition up from Mac OS 9.2.2, the partition sizes may be a maximum of 200 GB. If you have a drive that is larger than 200 GB in size, you will need to create multiple partitions with no single partition exceeding 200 GB in size."

Now, it may be that the 200GB limit doesn't apply to Standard-formatted partitions, because they contain far, far fewer blocks than Extended volumes of the same nominal capacity. But on a very large Standard drive, each block might be 1MB or even larger, while on an Extended drive each block is only 4K. What that means in real life is that on a Standard drive, a tiny 5K text file might occupy 1MB of disk space, while on an Extended drive, the same file would occupy only 8k. On a Standard volume, that file wastes 248 times as much space as it actually needs! A 1201K file on the same Standard volume would occupy 2MB, but on the Extended volume it would only occupy 1204K. The more small files a large Standard volume contains, the more of its nominal storage capacity is simply wasted. And the maximum number of files it can contain (65,000) is tiny compared to the number that can be stored on an Extended volume. So you really don't want to use Standard format, even if you only run Mac OS 9 and not OS X. The real-life storage capability of your drive will be radically diminished if you do.

As for the idea of partitioning the drive into two FAT32 volumes smaller than 200MB, that won't work for the reason I cited in my previous post: The PC-based partitioning scheme used to divide a drive into two or more FAT32 volumes is unreadable by OS 9. Similarly, the Mac-based partitioning scheme used to divide the same drive into two Mac OS Extended (or Mac OS Standard, for that matter) volumes is unreadable by Windows. The two operating systems can't read each other's partition maps. So no matter which computer you use to partition the drive, the other computer won't recognize the partitions. This is why it's essentially impossible to create a drive that has both FAT32 and Mac OS partitions on it, and why a cross-platform drive must therefore be a single unpartitioned FAT32 volume.

While it's my understanding that PCs will commonly balk at the idea of creating a FAT32 volume larger than 32GB, I've also been given to understand that if such a volume is created, the same PC will be perfectly happy to use it. And a Mac is quite happy to format a FAT32 volume larger than 32GB, at least if it's running OS X. What I'm not sure about is whether Mac OS 9 can format and use a FAT32 volume larger than 200GB, which is exactly what your situation requires. Maybe you can give that a try and let us know how it turns out.

Essentially, you are correct and we can't eat this cake and still have it. But there are three points I notice that need clarification. Two I am sure about, the third I am just guessing:

"While it's my understanding that PCs will commonly balk at the idea of creating a FAT32 volume larger than 32GB,..."
Actually, the problem is that Windows XP Setup program, using its format option, cannot creat FAT32 volumes larger than 32GB but you can create these partitions with a Windows 98 or ME CD and then install using the Windows XP CD.

"This is why it's essentially impossible to create a drive that has both FAT32 and Mac OS partitions on it..." Can't you create two FAT32 partitions in Windows, and then use Mac OS X Disk Utility to erase one volume to Mac Extended?

"and why a cross-platform drive must therefore be a single unpartitioned FAT32 volume." I think you mean to say "and why a cross-platform Windows-OS 9 drive that you want to both read from and write to must therefore be a single unpartitioned FAT32 volume or two volumes less than 128 GB each" since you could read from an NTFS drive in Mac OS X and you could read and write FAT32 volumes less than 128GB.

Actually, the problem is that Windows XP Setup program, using its format option, cannot creat FAT32 volumes larger than 32GB but you can create these partitions with a Windows 98 or ME CD and then install using the Windows XP CD.

You may be right: I was only repeating from memory something I thought I had been told. I may have been told wrong or remembered wrong, and if so, I'm happy to be corrected.

Can't you create two FAT32 partitions in Windows, and then use Mac OS X Disk Utility to erase one volume to Mac Extended?

No, I don't think so. I don't think Disk Utility will recognize the Windows partitioning scheme or, consequently, see any partitions. If I'm correct, all DU will see is an unreadable disk that needs to be formatted. If you have a spare hard drive you can experiment on, by all means give your idea a try, and let us know what you learn. I would do so if I had such a drive, but mine are committed to other uses: I can't format and partition one on my wife's PC to find out what would then show up on my Mac.

I think you mean to say "and why a cross-platform Windows-OS 9 drive that you want to both read from and write to must therefore be a single unpartitioned FAT32 volume or two volumes less than 128 GB each" since you could read from an NTFS drive in Mac OS X and you could read and write FAT32 volumes less than 128GB.

No, I meant what I said. A true cross-platform drive is one that can be read and written to on each platform, and the platforms we were talking about were Windows and OS 9.

Disk Utility and Drive Setup are unable to partition a drive if DOS format (FAT32) is selected. They can only format a DOS disk as a single unpartitioned volume. So you can't create multiple DOS partitions with a Mac, and if you do so on a PC, the Mac won't read them.

Yeah, that XP CD versus Win95/ME CD format issue is absolutely true; gone there, done that. Microsoft has their oddities. we just try to keep our heads above their ever-changing tide.

In OS X (maybe starting with 10.2?), multiple FAT32 partitions can be seen, mounted, written to if they are not too large. I use my USB drive with 2 FAT32 partitions in both Windows XP and OS 10.2.8 almost every day. I even wanted to erase one partition on my Mac and keep it FAT 32 but the Disk Utility had no option to leave it FAT32. I seem to remember (can't confirm it now as I recently erased my OS X internal drive and my CD-RW drive chose that moment to flake out) that Disk Utility did offer to erase one partition as Mac OS Extended. But I didn't as that would have left me with half the drive unusable in Windows XP so I formatted that one partition in Windows XP.

With respect to the recognition on a Mac (in OS X 10.something or better) of a drive that contains multiple FAT32 partitions created on a Windows box, I stand corrected. Thanks for the conclusive info, TRP.