Carbon itself was a concession, if you look at the earlier Rhapsody and OS X Server releases, it was pretty clear that they were planning on using the "Yellow B

Carbon itself was a concession, if you look at the earlier Rhapsody and OS X Server releases, it was pretty clear that they were planning on using the "Yellow Box" environment (Basically OpenStep) as the primary system, with the "Blue Box" emulation layer as the only way to run Classic software. Then a revolt from developers (apparently especially Adobe and Microsoft) and the reality of how much a Display PostScript license would cost relative to a PC set in, and OS X happened with it's in-house windowing system and Carbon for easy porting of well-behaved Classic software. See http://www.roughlydrafted.com/RD/RDM.Tech.Q1.07/4B800F78-0F75-455A-9681-F186A4365805.html http://www.roughlydrafted.com/RD/RDM.Tech.Q1.07/4B800F78-0F7... Also, early versions of OS X (IIRC though 10.4) were perfectly happy to install and work on UFS, the installer would even help you do so. From the user end, the problem with running OSX on UFS was that... a bunch of sloppy software broke on case-sensitive volumes. Famously, Adobe's entire suite wouldn't even install on case-sensitive volumes (see https://helpx.adobe.com/creative-suite/kb/error-case-sensitive-drives-supported.html https://helpx.adobe.com/creative-suite/kb/error-case-sensiti... I think it's still unfixed to this day). This is probably also the reason why despite Apple finally getting a modern file system... APFS has and defaults to a case-insensitive mode in opposition to essentially every other modern FS.