Mac Pro Special Report: PCI Express slots explained

Apple has posted a Knowledge Base document offering some interesting details about the PCI Express (PCI-E) slots found in the Mac Pro.

All four of the Mac Pro's PCI-E slots are 16-"lane" or "x16" slots. PCI-E cards will work in slots that are at least as large as the card is. This means that the "x16" slots in the Mac Pro computer also supports "x1" and "x4" cards.

Apple states "However, all four slots cannot simultaneously support four cards that implement the same lane configuration. Only one slot actually has 16 lanes going to it?you can put a x16 card into a slot that is only using one lane and it will operate properly, but it will operate more slowly than the same card in a x4, x8 or x16 slot."

Apple also explains the the Expansion Slot Utility, which is located in /System/Library/Core Services. This utility allows you to configure the PCI-E expansion slots and how many lanes each slot will support

An example graphic in the Knowledge Base article shows a "x16" graphics card occupying the first slot, and the other slots are configured to support an "x1" card in slot two and "x4" cards in slots three and four.

Index:

• AirPort and Bluetooth must be installed by service provider
• Apple Hardware Test issues
• Audio problems: Line out settings, distortion
• Blu-ray drive support
• Boot Camp issues: Getting proper SATA throughput, more
• Do-it-yourself manuals
• External device problems: System hangs, startup/shutdown/sleep problems, more
• Freezes during heavy disk activity
• Graphics card support
• Keyboards: Use of third-party devices can cause problems
• Memory (RAM): Usage of third-party modules; more
• Network transfer freezes
• PCI Express slots explained
• Power supply failures
• Technical notes: Processors are upgradeable, model string identifier, more

Resources