Yes, Win32 is just one personality, but a required one. OpenNT, Interix, SFU, SUA will ride alongside Win32. And of course there was the official OS/2 personality.
100%. Russinovich, who now heads up Azure, co-wrote many of the follow-on books, and David Solomon, who co-wrote the NT kernel, co-wrote the first few. The latest version of this book covers Windows 10/Server 2016. They are very, very good.
Or Inside Windows NT, if you want "version 1" of the Internals series. Or read the Windows NT OS/2 Design Workbook - https://computernewb.com/~lily/files/Documents/NTDesignWorkb....
Yes, Win32 is just one personality, but a required one. OpenNT, Interix, SFU, SUA will ride alongside Win32. And of course there was the official OS/2 personality.