Install PCIe cards in your Mac Pro (2019)

Learn about the PCIe slots on your Mac Pro (2019) and how to install additional cards.

Card capacity and size

Mac Pro has eight PCIe x16* sized slots that accept many different types of PCIe cards:

  • Slot 1: up to x16 lanes (double-wide)
  • Slot 2: up to x8 lanes (double-wide)
  • Slot 3: up to x16 lanes (double-wide)
  • Slot 4: up to x16 lanes (double-wide)
  • Slot 5: up to x16 lanes (single-wide)
  • Slot 6: up to x8 lanes (single-wide)
  • Slot 7: up to x8 lanes (single-wide)
  • Slot 8: up to x4 lanes (half-length)

Slot 8 is x4 in size.


Mac Pro Expansion (MPX) Modules can use up to two slots each – in slots 1-2 and slots 3-4. Mac Pro comes with the Apple I/O card preinstalled in slot 8 which contains two Thunderbolt 3 ports, two USB-A ports and a 3.5 mm headphone jack. Learn about PCIe cards you can install in your Mac Pro (2019).

Check available slots

To check the status of each slot, choose Apple menu  > About This Mac, then click the PCI Cards tab.

By default, Mac Pro automatically balances bandwidth between all of the cards across the two PCIe pools. You can use Expansion Slot Utility to make manual adjustments to pool allocations.

Installing PCIe cards

Learn how to remove the housing of your Mac Pro and install a PCIe card. 

Remove the housing

  1. Shut down your Mac Pro.
  2. Wait approximately 5-10 minutes for the computer to cool down.
  3. Unplug all cables except the power cable from your computer.
  4. Touch the metal housing on the outside of Mac Pro to discharge any static electricity, then unplug the power cable.
    Always discharge static before you touch parts or install components inside your Mac Pro. To avoid generating static, don't move around the room until you finish installing the cards and slide the enclosure back onto the computer.
  5. Flip the top latch up, then twist left to unlock the housing.
  6. Lift the housing straight up and off of Mac Pro. Carefully set it aside.
    Mac Pro won't turn on when its cover is removed.

Install a PCIe card

  1. Slide the lock to the right.
  2. Using a Phillips-head screwdriver, unscrew and remove any brackets and slot covers covering the slots where you want to install your card. 
  3. Remove your new card from its static-proof bag and hold it by its corners. Don't touch the gold connectors or the components on the card.
    Use only PCIe modules that are safety certified (CSA, UL or equivalent) and specifically state that they are compliant with the industry standard PCIe specification. Use of non-certified compliant modules may not keep different input power sources separated, resulting in a possible burn hazard.
  4. Make sure the card pins are in line with the slot as you insert the card into the PCIe slot.
  5. Slide the lock to the left.
  6. Reinstall any side brackets you removed, then tighten the screws on the bracket.

Reinstall the housing

  1. Carefully lower the housing over Mac Pro.
  2. After the housing is fully seated, twist the top latch right and flip it down to lock it.
    Top: Locked position (dots match)
    Bottom: Unlocked position (dots do not match)
  3. Connect the power cable, display and any other peripherals.
  4. Press the power button. 

If your PCIe card requires a driver, learn how to turn on third-party drivers in macOS.

Anytime you add or remove a card from your Mac Pro, Extensible Firmware Interface (EFI) dynamically manages PCIe lane allocation to balance bandwidth for your cards. If you want to manually manage throughput, you can use Expansion Slot Utility to adjust each card's pool allocation.

If you install two Radeon Pro Vega II MPX Modules, you can connect them together using Infinity Fabric Link. Learn how to connect two Radeon Pro Vega II MPX Modules.

Turn on third-party drivers

Some third-party PCIe cards require a driver before they can be used in macOS. After you install a driver for a third-party PCIe card, restart your Mac Pro, then turn the driver on:

  1. Choose Apple menu  > System Preferences, then click Security & Privacy.
  2. Click the lock  and authenticate as an administrator.
  3. Click the Allow button.
  4. Restart your Mac.

Use Expansion Slot Utility

When you install or remove PCIe cards on your Mac Pro, EFI detects the cards in each slot and allocates bandwidth between the two pools to maximise throughput. Expansion Slot Utility lets you view and change how your cards are allocated.

Use Automatic Bandwidth Configuration

By default, your Mac Pro uses Automatic Bandwidth Configuration to automatically manage how the cards are allocated to each of the two pools.

Assign pool allocations manually

If you want to manually assign the pool allocations for your cards, turn off Automatic Bandwith Configuration and choose a pool for each card. For example, you might want to give a single card 100 per cent allocation of pool A.

Whenever you make changes to pool allocation, Expansion Slot Utility prompts you to save your changes and restart your Mac before they take effect.

Get help installing PCIe cards

Learn what to do if you get a PCIe card misconfigured error or your Mac Pro won't turn on after installing a PCIe card.

Resolve PCIe card misconfigured errors

If your PCIe cards can be installed in different slots to provide better performance, you'll see a PCIe card misconfigured notification after your Mac Pro starts up:

macOS notification indicating a PCIe Card Misconfigured error stating that the PCIe card in slot 6 is not placed in an optimal slot with Close and Learn More buttons.

Click Learn More, which opens the PCI Cards tab of About This Mac. Then, click Expansion Slot Utility to view recommendations on how you should reconfigure your cards.

If your Mac Pro doesn't start

If your Mac Pro doesn't start up and the status indicator light flashes amber twice after installing a PCIe card, the card might not be compatible with your Mac Pro or you might have too many 32-bit PCIe cards installed. 

If you recently installed one or multiple PCIe cards, remove each card one at a time and try turning on your Mac Pro after each card removal. 

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