Display for PowerMac 7100/80 Power PC

On this page, scroll down to the "Cable, HDI45 to DB15, Display Adapter." That converts the HDI-45 interface to an Apple DB-15 monitor port. To use a VGA display having an HD-15 plug, you'll need to connect a Mac-to-VGA adapter to the HDI45-to-DB15 adapter. Here's that adapter. Hopefully, your father-in-law's 7100/80 has 2 MBs of VRAM installed, so that a 17" CRT display can have a fast refresh, acceptable resolution, and good color depth. If the 7100 only has 1 MB of VRAM installed, you're really limited to a 15" or smaller CRT. Current LCD displays are out of the question, given the video circuitry of the NuBus Macs. If the 7100 had PCI slots, there would be so many more modern available options.

There are no VRAM slots on the motherboard. Additional VRAM can only be added, if the video card for it is installed in the PDS slot. From a web site dedicated to the Power Mac 6100's, this page is informative. If the HPV (High Performance Video) card is installed in the 7100's single PDS slot (beside the 3 white NuBus slots), you'd see an Apple DB-15 monitor port on the back of the computer, vertically oriented. If so, check to see if the (4) VRAM slots on the card are filled. If they are, the VRAM is maxed out at 2 MBs. You'll only need to buy the Mac-to-VGA adapter, if the card is present. If there is no card installed and you connect through the HDI-45 port with adapters, you're relying on 1 MB of DRAM for video support. It's unfortunate that you may end up paying as much for the adapters as a slightly newer and better-equipped Power Mac would cost you at a thrift store. If you need a CRT display, I'd also suggest checking a thrift store for one, because many people are upgrading to LCD displays and donating their older/still-functioning monitors.