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Ole Juul
January 17th, 2011, 07:27 PM
My main DOS box has a VGA card and an MDA card. Suddenly there was no video on either one. I've rebooted several times and nothing. I did check connections, but being two separate cards and cables etc, it was unlikely to be there anyway. I'll unplug the cards and try a new VGA card as my next step unless someone has a good idea. Booting from a floppy doesn't do anything either, so it is not my config. Everything else seems to work because I can issue commands from the keyboard, such as start a server and ping the machine from elsewhere.

This happened just now while testing the TELNED program. Perhaps it's malware lol. Seriously, what could cause this? Any suggestions?

It's a P-133 board.

vwestlife
January 17th, 2011, 08:13 PM
Maybe the BIOS got confused as to which card should be the default, and ended up disabling both. Try removing one of the two video cards to at least get one working, before adding the second one.

Ole Juul
January 17th, 2011, 08:55 PM
OK, I got back to this after dinner armed with a replacement VGA card and a screwdriver. However, the first thing I did was just pull the mono card. That did it! Phew! I rely heavily on this machine and wasn't looking forward to dealing with this right now.


Maybe the BIOS got confused as to which card should be the default, and ended up disabling both. Try removing one of the two video cards to at least get one working, before adding the second one.

Thanks for posting. I think you may indeed be right. There is something I don't understand here and the BIOS confusion may explain it.

After I then had video I first went into the BIOS to see what I could see (or fiddle). Under "Bios Feature Setup" I see "Video Ram Bios Shadow" with the choice to enable or disable. This is followed by several address ranges starting with C8000. All these ranges are disabled. However the general choice of "Video Bios Shadow" at the top is ENabled.

I don't quite understand this because I would think that if that was enabled it would imply that the additional mono range starting at B8000 would then be shadowed. Bear in mind here that I don't really know what that means in this case. Anyway, I DISable this and plug in the MDA card again. Upon booting up I get three beeps (IIRC, long, short, short) indicating video error. However it works correctly and I can switch between mono and colour without problem. Next I go back to the BIOS and ENable "Video Ram Bios Shadow" again. Upon reboot, there are no beeps and the mode switching still works. I assume then that this is the right setting.

All this would indicate that you are correct vwestlife, but how could this happen?

Chuck(G)
January 17th, 2011, 09:39 PM
Video BIOS shadowing works by copying the contents of the video ROM into RAM and then mapping the original ROM out. The idea is that the BIOS routines are now running from (much faster) RAM.

This should have nothing to do with the MDA because an MDA doesn't have a BIOS ROM onboard--support for the MDA is supposed to be in the main BIOS itself.

I suspect that if you turn BIOS caching on without specifying a range, the BIOS simply probes the video area C0000-C7FFF and automatically selects what to copy. I have no idea what's causing your system to fail when the option is disabled.

Another setting that you sometime see is "Video RAM Cachable" which can also usually can be disabled.

Ole Juul
January 17th, 2011, 10:13 PM
Thanks for the info Chuck. Caching or otherwise will probably make no difference on my machine anyway since it is so fast in relationship to the nature of the software that I run. I/O is the limitation here.


Chuck(G): I suspect that if you turn BIOS caching on without specifying a range, the BIOS simply probes the video area C0000-C7FFF and automatically selects what to copy. I have no idea what's causing your system to fail when the option is disabled.

It doesn't actually fail (that was just the one time thing) it just gives the video error beeps. The beeps occur as described above, and always upon exit from the BIOS setup. I occasionally (not always) also get them when I reboot - before it goes to the boot phase. Perhaps this BIOS simply does not like (probably didn't expect) having two video cards. It has worked fine for months until now.

Here are the other relevant choices I have in my BIOS, which is Award 7/14/97 on an Asus TXP4 board.

Standard Setup:
Video: choices are EGA/VGA, or CGA, or MDA (set to VGA)

BIOS Features Setup:
PCI/VGA Palette Snoop: Enabled, or Disabled (set to Disabled)

Chipset Feature Setup:
Video BIOS Cachable: Enabled, or Disabled (set to Enabled)