4 lane vs 8 lane vs 16 lane slot - Radeon X1900 on Mac Pro

We were wondering how much speed is "scrubbed" off when you run a graphics card in a slower PCI Express slot. This should be of interest to some of you who plan to run more than one GPU in your Mac Pro. When you add or move any PCI Express card, the Expansion Slot Utility is invoked at startup, offering you choices as to how to configure each of the four slots. Since only slot one runs in 16 lane mode (x16), then you must decide how fast the other slots are to be configured. And your choices are limited.

We ran various graphics intensive apps at 1920x1200 High Quality to see how much faster a Radeon X1900 XT runs in the 16 lane (x16) slot as opposed to being installed in a 4 lane (x4) and an 8 lane (x8) slot. Our tested unit was a Mac Pro 3GHz with 16GB of RAM.

Quake 4 (1.20) Settings: High Quality, Widescreen, No Vsync, No Anti-Aliasing, all other advanced settings enabled including multi-processor mode.

Doom 3 (1.3a) Settings: High Quality, No Vsync, No Anti-Aliasing, all other advanced settings enabled.

Halo (UB) Settings: All parameters enabled and at highest quality except Lens Flare which we had at a low setting. No FSAA. Sound disabled.

UT2004 (build 3369.2) Settings: Using SantaDuck Toolpak, we ran the Inferno Botmatch with Graphics Enabled, Sound Enabled, and Maximum Quality Settings.

ANALYSIS
Based on our testing, your penalty for running a Radeon X1900 XT in an 8 lane slot is only slight compared to the 16 lane slot. But running it in a 4 lane slot scrubs off a significant amount of speed.

RUNNING TWO RADEON X1900 XTs
We know of at least one university running two Radeon X1900 XTs in their Mac Pro. They are using them to drive three 1920x1080 projectors. I'm not sure now many Mac Pro users would want two X1900s in their Mac Pro but there are two things you should know if you do:
1) The PCI Express bus can handle a total of 300 watts. Each Radeon X1900 XT requires a peak of 132 watts. So two of them equals 264 watts. You should be okay if you don't add any other PCIe cards -- especially since both cards are pulling power from the special six pin motherboard connector instead of the bus!
2) To get the best performance from both high-end cards, we recommend installing the second X1900 in slot 2 (since slot 1 is double wide) and using the Expansion Slot Utility (in System/Library/CoreServices) to configure both slot 1 and 2 to run in 8 lane (x8) mode. (Though slot 4 can be configured to run at x8 with slot 1 running at x16, the X1900's heatsink is too thick to allow it to fit there. And slot 3 can only be configured as x4.)

We're hoping Apple will provide better configuration options for two high-end graphics cards in the next generation of Mac Pros.

DETUNED RADEON X1900 XT
Though the Radeon X1900 XT "whups" the GeForce 7300 GT, we were surprised to find out that Apple "detuned" the X1900 XT to run at 600 core clock speed and 650 memory clock speed. In the Windows PC world, a Radeon X1900 XT typically runs at 625MHz core clock speed and 725MHz memory clock speed. And it does NOT dynamically "up-clock" when you run OpenGL 3D apps as in the case of the MacBook Pro 17".

WHAT ABOUT THE QUADRO?
The only other card "high end" GPU available for the Mac Pro is the $1650 Quadro FX 4500 which Apple is promoting for "high-end scientific visualization." It would be overkill for most applications including games. And if you look at the specs listed on the Mac Pro Graphics Page, the X1900 beats it in two out of three performance specs. Both cards feature 512MB of DDR3 and both support up to two 30" Cinema displays.

(We actually have a Quadro FX 4500 in the lab but it was purchased with our Quad-Core G5 and only works on a G5 with PCIe slots. If you know someone with a Quadro FX 4500 in their Mac Pro, have them contact us.)

Can you use Windows PC PCIe graphics cards in a Mac Pro? NO. That's because Apple uses special code in the Extensible Firmware Interface (EFI). Get the whole scoop in THIS ARTICLE. Nor will the G5 Power Mac PCIe cards work in your Mac Pro -- for the same reason.

Can you use Dual-Core G5 Power Mac PCIe graphics cards like the GeForce 7800 GT and Quadro FX 4500 in a Mac Pro? No. They are not compatible with the Mac Pro.

OTHER ARTICLES ON THE MAC PRO by BARE FEATS

Mac Pro 3D Game "Slug Fest" -- the Radeon X1900 vs GeForce 7300 vs two G5 Power Macs with high-end graphics cards

Mac Pro with X1900 XT running Motion 2 and iMaginator

Mac Pro versus Quad-Core G5 -- Updated Photoshop CS2 results under 10.4.8

Original Test Results on Mac Pro for Photoshop CS2, After Effects 7, iMovie HD, Final Cut Pro, FileMaker 8.5, and Cinebench 9.5

Fastest Boot Drive for the Mac Pro

What You Should Know About Mac Pro Memory

WHERE TO ORDER YOUR MAC PRO MEMORY
You can order extra Mac Pro memory from Apple USA when you custom order your Mac Pro, though it might delay delivery. Plus, we think Apple charges too much for their memory upgrades.

We recommend getting your memory upgrades from third party vendors. In our initial Mac Pro testing, we used kits provided by Other World Computing. They are a good source for quality memory at a reasonable price. Plus OWC has a "Trade In Your Factory Memory" REBATE program.

TransIntl.com is shipping Mac Pro memory with Apple suggested heat sink specs. They took great care to engineer their heat sinks for maximum thermal efficiency using 6 fins on each side (versus 4 on the Apple factory modules) and special aluminum alloy. We tested these and can vouch that their heat sinks are truly efficient in absorbing and dissipating heat.

MaxUpgrades offers their unique "MacSink" design for a heat sink (using 2 clips instead of 4) which results in more fin area exposed to the airflow. We've tested them and they are very effective. MaxUpgrades will sell you the memory with the heat sink or just the heat sink. Their prices are very competitive, too.

We also tested the Data Memory Systems Mac Pro memory with conventional heat spreaders. It ran an average of 10 deg F warmer than the memory with "fat finned" heat sinks. DMS is also offering memory with Apple approved" heat sinks as an option.