Windows 95 used "32-bit file access" (an option in Windows 3.1) by default. Which meant it had its own file drivers and was, in effect, a full 32-bit OS chain-loaded from DOS. However, in order to keep the "DOS box" working and make sure DOS knew about all the changes to the file system, Windows 95 had to update the DOS structures in memory also. Which made it an even bigger mess of hacks than we realized.