macOS Catalina Brings Back Expansion Slot Utility App Before the New Mac Pro Launch

George Herman
George Herman
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As Apple reported at WWDC 2019, the new modular Mac Pro will be released this fall. Yet, ahead of its release, the company launched the second developer beta of macOS Catalina where Apple brought back the Expansion Slot Utility application, allowing users to manage the PCI expansion options of the Mac Pro.

Originally, Expansion Slot Utility was available on the early Intel-based Mac Pros, however, Apple ceased the app support in 2008. This happened because the early 2008 Mac Pro model didn’t have a configurable PCIe setup as all lanes had fixed assignments. Nevertheless, now with the all-new Mac Pro, Apple is bringing the Expansion Slot Utility application back again.

Steve Moser and Guilherme Rambo were the first who wrote on Twitter that the Expansion Slot Utility is hidden in the second developer beta of macOS Catalina. In the application, all Mac Pro users will be able to manually assign bandwidth between pools or enable automatic bandwidth configuration. The second option will let the Mac Pro itself assign bandwidth between PCI Expansion accessories.

Expansion Slot Utility app will also inform users when their installed PCI cards are not arranged in a configuration which will produce the best performance. In this case, the application will offer suggestions on where to move specific cards, so that users can improve the performance.

The new Mac Pro will be available this fall and it will include eight PCI Expansion expansion slots in total, featuring single-wide slots, double-wide slots, and a single half-length slot. Users can read what Apple explains about the new Mac Pro’s expandability below:

Two MPX Modules or up to four PCI Express card slots

Each MPX bay provides:

  • x16 gen 3 bandwidth for graphics
  • x8 gen 3 bandwidth for Thunderbolt
  • DisplayPort video routing
  • Up to 500W power for an MPX Module

Alternatively, each MPX bay can support:

  • One full-length, double-wide x16 gen 3 slot and one full-length, double-wide x8 gen 3 slot (MPX bay 1)
  • Or two full-length, double-wide x16 gen 3 slots (MPX bay 2)
  • Up to 300W auxiliary power via two 8-pin connectors

Three full-length PCI Express gen 3 slots

  • One x16 slot; two x8 slots
  • 75W auxiliary power available

One half-length x4 PCI Express gen 3 slot with Apple I/O card installed


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