Mac Video Cards

For the most part, the difference is the video ROM and possibly the size of the chip that stores the ROM. While there are some PC video cards that can be flashed to be used on the Mac (ATI Radeon, Voodoo 3), others can not be. Of course, drivers also play an important part in getting a video card to work in a Mac. As an example, I can guarantee if I grabbed some el cheapo PC PCI video card from my parts bin and put it in one of my Macs that it won't work because there are no Cirrus Logic, S3, or Trident drivers for the Mac for those cards and they have a PC video ROM in them.

Correct me if I'm wrong on this, folks!

You got it pretty much right

There are some differences in newer cards when it comes to mac vs pc. Mac cards have different features then pc cards in some cases, but for the most part, the cards are fairly similar from a hardware point of view. The ROM for each is obviously very different, as the MacOS accesses the video card in a different way then windows and linux.

As far as drivers go, windows, linux, and the MacOS all have very different drivers. Parts of linux drivers are derived from the windows drivers, but this is only the very base set of instructions. When it comes to driver based features, macs have many features windows and linux do not have. OSX supports real multi monitor support, unlike windows (multi monotor on windows still sucks, even after all this time). ATI cards on macs have access to 'versa vision'. This allows you to rotate your screen any way you like, so if you want a portrait display, flip your display onto its side, and rotate the screen.

For nVidia cards, all you get are basic drivers, no fancy features. With an ATI, you can turn on FSAA, Anistropic Filtering, adjust the quality, etc etc from the ATI control panel, as well as hook up a TV and set its settings to your card. nVidia cards on the Mac have none of these features. And since Apple is the one who makes the drivers (they get a base code base from nVidia however), I dont see them (Apple) taking the extra step to bring these kinds of features to the nVidia based cards.