Some time ago, I thought it would be useful to understand exactly what is the difference between CD-ROMs recorded in the old High Sierra format versus the ISO 9660 standard. This was in part spurred by the fact that I have a number of CD-ROMs/images that use the High Sierra format (Microsoft Programmer’s Library, some IBM Developer Connection issues, OS/2 Warp 4, and more) that both macOS and Windows 10 refuse to mount. The other part of my motivation was the usual insatiable curiosity.
I had no idea about the existence of this different format.
Doubtless ditching CD-ROM High Sierra Support was a Microsoft attempt to remove kruft along with hiding the ability to mount a floppy drive. I don’t know about built in but USB floppy drives still work. I have no idea about external CD-ROM format support. Of things to remove these seemed like an odd choice.
Modern Windows still supports floppy drives, and it is even recommended for certain imaging tasks – they’re still used in retro computing circles for writing floppies from other 8-bit or 16-bit computers.
I think the minimum supported in Windows is actually 720k floppies – 360k floppies aren’t supported.
If you’re using Windows and writing floppies on a regular basis, you’re probably running an older Windows version anyway. Windows 9x and a pre-P4 system is pretty much the gold-standard for floppy disks, since most floppy-based software required DOS. By the time XP came around, software was largely distributed on CD-ROM.
The spam protection on OS/2 Museum doesn’t like either of my browsers, so I couldn’t say it there, but there are actually a couple of other interesting early CD formats:
1. Not-quite-standard ISO9660 CDs with 512-byte sectors. (I’ve got one of these. FreeDOS’s MSCDEX equivalent doesn’t like them and Linux will only mount them with
-o loop,block=512.)2. Adaptec’s short-lived alternative to the Joliet extensions to support Windows NT 3.5a: Romeo.
There’s loads of obscure, non-standard CD-ROM formats. Most Mac OS software CD’s were formatted as HFS.
I don’t really consider HFS on CD-ROM to be obscure, given that I’ve got tons of ISO/HFS hybrid discs and mkisofs/genisoimage supports creating them.
I can only think of two CDs in my collection of over a thousand that are High Sierra and one with 512-byte sectors. None are Romeo… at least, that I’m aware. It’s possible that Kubuntu 16.04’s inability to read High Sierra was a transient thing and I successfully backed up more High Sierra discs among my collection on earlier Linux versions.
Likewise, mkisofs/genisoimage has no support I can find for generating High Sierra, Romeo, or 512-byte ISO9660 discs….though that does remind me that I should dig out the old copy of Adaptec EasyCD that came with my very first CD-burner back in the late 90s and see if’s old enough to have support for making me a Romeo test ISO.
I have a number of old DOS games that have slightly non-compliant ISO filesystems, and many more that just have funky session data on them that a lot of modern drivers don’t like.
512 byte blocks was used as a Sun format (probably others too), I believe there are CD drives which can transparently translate from this to the standard block size (such as the CD drive that was shipped in the Sun Blade 150), but they are somewhat hard to find now, and if you don’t have one you can’t boot to those CDs. Consequently, you can’t boot non-512 byte sector CDs in those drives either, which is a huge pain for using some early 2000’s Sun computers