You can download a newer version of the Model 4 operating system from my
Web pages that accepts dates through 2011 or so. It's called LS-DOS 6.3.1.
It was put out by the same company that wrote TRSDOS 6 for Tandy, so it's
a compatible upgrade of the same code base, not a clone.
I think newer versions of the Model 4 say "Diskette?" at the top of the
screen if you try to boot with no diskette in the drive. At least newer
versions of the Model III do that. (The III and 4 work with the same boot
ROM.)
Yes, it's nerve-wracking having to remove that cover with extreme care
to avoid breaking the neck of the CRT...
Tim Mann tim.mann(a)compaq.com
http://www.tim-mann.org
Compaq Computer Corporation, Systems Research Center, Palo Alto, CA