I'm trying to think of a good use case for exploring the NT 3.5 source code but I can't really think of one. It had the Windows 3 user interface and a number of enterprisey things like telephony (TAPI) and UPS control, but was overall pretty bare-bones.<p>I remember a few quirks. I lacked a CD drive and borrowed one to install NT 3.51. When I gave the CD drive back, NT wouldn't boot. It turns out that it installs ATAPI.SYS if you have a CD, which won't boot without it. It installs ATDISK.SYS if you don't have a CD.<p>System administration was pretty clumsy. I really began to appreciate the text file based UNIX philosphy over the point-and-click Microsoft approach. I had been dual booting NetBSD and OS/2 2.1 before that.<p>Nonetheless it was solid compared to Windows 3.1 and 95. Perhaps being limited to what it was, it'd be easier to study the native api and how it was being accessed by the several subsystems (Win32, OS/2, POSIX). A much lighter version of NTFS was running on it. I remember at the time you needed a windows source license to write a filesystem driver. I was using Visual C++ 4.0. 100Mbit ethernet was fast for the time and I was a little jealous of people using 155Mbit ATM.