Using old video card in Mac Pro Tower

Economically? Maybe...

Depending on the video board your Mac Pro has (it should be a nvidia GT 120 or a ATI 4870) and what interface the display requires, you may be able to find an adapter.

The G4 PowerMacs had a PCI bus for expansion, two generations behind the PCIe bus in your Mac Pro.

The only way I know of to bridge the generation gap involves a PCIe-to-PCI adapter, something I've never tried.

hope this helps

RE: Mac Pro Replacement Graphics cards

1) Apple brand cards,

2) "sold in the Apple store" cards, and

3) "Mac Edition" cards ...

... show all the screens, including Boot up screens, Safe Mode, Installer, Recovery, debug screens, and Alt/Option boot screens. At this writing, these choices include:

1) Apple brand cards:

• Apple-firmware 5770, about US$250** works near full speed in every model Mac Pro, Drivers in 10.6.5

• Apple-firmware 5870, about US$450

2) "sold in the Apple store" cards

• NVIDIA Quadro 4000, about US$1200

• NVIDIA Quadro 5000, about US$2500

3) "Mac Edition" cards -- REQUIRE 10.8.3 or later:

• SAPPHIRE HD 7950 3GB GDDR5 MAC Edition, about US$480** Vendor recommends Mac Pro 4,1

• EVGA GTX 680 Mac Edition, about US$600

The cards above require no more than the provided two 6-pin aux power connectors provided in the Mac Pro through 2012 model. Aux cables may not be provided for third-party cards, but are readily available.

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If you are Meet ALL of these:

• running 10.8.3 or later AND

• don't care about "no boot screens" etc AND

• can re-wire or otherwise "work out" the power cabling, THEN:

You can use many more cards, even most "PC-only cards"

.