I once tried to make a bootable CD for Windows NT 3.51 before. After booting to a certain stage, I couldn't find the files.
After thinking carefully, the El Torito standard for CD-ROM booting was proposed in 1995, and Windows NT 3.51 was also released in the first half of 1995. At that time, there were no bootable CDs in the world, so Windows NT 3.x couldn't directly support bootable CDs. It seems that the first version of Windows 95 also had to be booted from a floppy disk first, and then the CD-ROM driver was loaded to install it.
As for the second question, I always install the NT system from DOS like this, and there's no need to make a floppy disk. The /B option for winnt has been effective since Windows NT 3.5, and it's no longer needed starting from Windows 2000. Here are the parameter explanations for winnt /? of Windows NT 3.51:
Installs Windows NT.
WINNT sourcepath] tempdrive] inffile]
] ]
/Ssourcepath
Specifies the source location of Windows NT files.
Must be a full path of the form x:\ or
\\server\share.
The default is the current directory.
/Ttempdrive
Specifies a drive to contain temporary setup files.
If not specified, Setup will attempt to locate a drive for you.
/Iinffile
Specifies the filename (no path) of the setup information file.
The default is DOSNET.INF.
/O Create boot floppies only.
/OX Create boot floppies for CD-ROM or floppy-based installation.
/X Do not create the Setup boot floppies.
/F Do not verify files as they are copied to the Setup boot floppies.
/C Skip free-space check on the Setup boot floppies you provide.
/B Floppyless operation.
The /B means floppyless operation. After copying files under DOS and restarting, it starts the character interface installation stage from the hard disk.