[ct-user] CTDos crashing after Restarting in DOS Mode

[John Bednar]

I recently changed my ham radio computer and I immediately learned
that I could no longer start CTDos using the Win98 Start | Shutdown
| "Restart in DOS" option. I have been using CTWin for several years
but it bothered me that I didn't understand what was causing this
problem.

In Dos with the above technique, CT it would crash immediately (even
before prompting for the filename). I tried several versions of
CTDos including CT9.27 and CT10.005 with the same results. The panic
crash message from CT9.27 was "Illegal Interrupt #07" along with a
short register dump. CT10.005 display a much larger panic crash
message which included "error(2001) exception 07 device not
available".

As a test, I found that I could successfully start CTDos in a
Windows DOS window but I knew this wasn't recommended so I continued
to experiment.

In steps, I removed all memory except 128M, removed autoexec.bat &
config.sys files, set all BIOS parameters from PCI to ISA, disabled
all caching & shadowing, disabled the USB ports, removed all ISA and
PCI cards except the video card but CT still crashed. I made a
bootable DOS disk from Windows and booted from it, CTDos still
crashed.

I was ready to give up but I tried one last experiment. I changed
the parameters on the hidden MSDOS.SYS and changed the BOOTGUI line
to BOOTGUI=0. This is documented on the CT Webpage and it prevents
Win98 from booting into the Windows environment from a cold start.
With this change, CTDos finally started without crashing! I tried
several DOS versions and they all started just fine. After replacing
the memory, sound card, network card, 4-port I/O card, and resetting
all the BIOS parameters, CTDos still starts just fine. 

Apparently, Win98 has a set of commands that it runs before
"Restarting in DOS mode". Something that Windows was setting on exit
was causing CTDos to crash. 

John
k3ct at fast.net