View Full Version : 16 bit card in 8 bit slot

September 25th, 2005, 02:04 AM
I've got a question about an old 8088 system that I bought today.

Obviously, being an 8088 it only has 8 bit ISA slots. All the 8 bit video cards that I have are EGA, and unfortunately I don't have any EGA monitors around here.

What would happen if I were to use a 16 bit VGA card in the 8 bit slot? I would've thought that it would be stupid to try, but the computer already had a 16 bit MFM controller in one of the 8 bit slots (looks like it's been in there for 20 years too, so I doubt it was put there by accident).

September 25th, 2005, 03:02 AM
Also, the video card in it (Paradise PEGA1A) has two RCA ports on the back. I believe that one of them is composite out, but can't get my TV to tune in to it.

There's a bank of 5 dip switches on the back of the card. Does anyone know how to configure it to enable the RCA ports?

September 25th, 2005, 04:06 AM
AFAIK the 16 b in a 8 bit slot only works with (some!) network cards.

September 25th, 2005, 08:27 AM
There were video cards that were 16 bits but could work in an 8 bit slot as well. And of course, there are true 8 bit VGA cards floating around. I have one in my PC 5150.

If your card has 5 dip switches it's not copying the IBM EGA card exactly - the IBM EGA card only has 4 dip switches.

The RCA jacks on the IBM EGA card (and the Paradise one) are non-functional. It's funny - IBM probably put them there planning on some sort of composite output signal, but didn't actually use them. And at the time IBM compatibility was so important that other people put the RCA jacks on their clone cards, even though they had no use!

September 25th, 2005, 08:49 AM
Thanks for the replies. If I tried it and it wasn't compatible, is it going to kill anything or just not work?

I'm starting to wish I never threw out my boxes of computer parts a few years back, they could come in handy now.

Terry Yager
September 25th, 2005, 09:33 AM
The EGA card can be configured to output CGA video. Try experimenting with the DIP switches.


October 3rd, 2005, 05:38 PM
I have a Paradise VGA card that can be used in an PC/XT or a PC/AT type slot. Presumably it'll run faster if employed in an AT, for only it can utilize the extra signals/pins.
I think the oldest machine I ever used it in is a Pentium 166MMX.
Not likely you'll damage anything plugging a 16-bit card into an 8-bit bus. It just won't work, unless it's a card like what I described.