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PCI vs. AGP graphics cards
Update: Added confirmation based on my experiences with the 9600.
In my recent post on my planned Mac upgrade, I mentioned I was going for an AGP graphics card instead of a PCI one. That may seem odd, since adding a PCI card means you can keep your old AGP card in the Mac and have two, without the need to buy an ADC->VGA adapter and taking advantage of the built-in card's VRAM.
But my rationale was that AGP is generally PCI with more direct access, and thus more speed (in layman's terms, for more detail, see the Wikipedia entries on PCI and AGP). And since my Mac is rather old, I didn't want to spend money on a significantly faster graphics card just to have it throttled down by the PCI bus if the AGP bus would have let me use it at full speed..
Additional information at XLR8YourMac names another reason to use an AGP card instead of a PCI card: Apparently, OS X only supports Quartz Extreme for AGP cards. There is a hack to turn it on for PCI, but the problem there is that a PCI graphics card thus Quartz-Extreme-ed may 'starve out' other devices on the PCI controller, like an SCSI card. It's supposedly less of an issue with Macs that have a 66 MHz bus, but my Clockwork only has 33 ... dang.
A thread on comp.sys.mac.hardware.video on the other hand claims that PCI and AGP graphics cards themselves weren't much different performance-wise, because most of the AGP advantages were not being used by current OSs, though another thread there mentions that you may have problems running DVDs on a PCI card.
|AGP 4x||PCI 33|
|Raw bus speed||266 MHz (1066 MB/s)||33 MHz (133 MB/s)|
newer PCI-X buses are same speed as AGP 4x
|Bandwidth||Dedicated to AGP slot||Shared by all PCI devices|
may starve them
(supposedly less problematic with PCI 66)
|Quartz Extreme||Supported||Requires Unsupported hack|
Hack broken since 10.3.7
|System RAM usage||Yes, but OSs don't take advantage||No|
|DVD Playback||No Problem||Apple DVD Player may not work|
on 10.4 "Tiger"
|Yes if the card supports (Smart)Shader 2.0||Unknown|
If you're in the market for a new graphics card, too, you might like this Page for comparing ATI Graphics Cards. nVidia has comparisons of their cards on the cards' pages themselves. And watch out that the new card supports CoreImage. Although most CoreImage effects will run on your CPU if the graphics card isn't powerful enough, this will obviously be slower, and the whole point for buying a new graphics card is a faster Mac, isn't it?
A list of supported graphics cards can be found in a FAQ in a MacRumors Forum Thread. There's also a less detailed one on Apple's site. According to that forum entry, all variants of the cards Apple specifies are supported as well (i.e. while Apple only mentions the 9600 XT card as being supported, a 9600 Pro or 9600 will do just fine). This is supported by threads Google Cache pulled out of AppleNova Forums, and by my experiences (I got myself a 9600 Pro and it worked). According to these forums, CoreImage requires a card capable of Shader 2.0 (ATI calls this SmartShader 2.0).