Apple Mac Pro: Does Expandability Really Matter?

Apple has announced its new Mac Pro professional desktop workstation, and it is 1/8th the volume of the old one. To get it so small, Apple had to remove one of the primary reasons to get a Mac Pro in the first place: There is no significant internal expansion space in the new 2013 Mac Pro.

Apple's upcoming Mac Pro is an enigma. No, really, there's a lot about the system we don't yet know, including exactly which Xeon processors will be available, which dual AMD FirePro GPUs will be in the system, and the ultimate pricing of the Mac Pro. What we do know is that the system comes with replaceable PCIe flash storage as the main drive, four DIMM slots for 1,866MHz DDR3 ECC memory, and that everything is built around a massive heat sink with a single fan for cooling. The system comes with a HDMI port, four USB 3.0 ports, and six Thunderbolt 2 ports. That's a lot of ports for external expansion, but that's not enough for the Mac Pro faithful, the ones that have been using PCIe adapters and rows of internal hard drives all these years.

External Expansion Is Doable
Yes, you can connect USB 3.0 drives, Thunderbolt hard drives, and PCIe to Thunderbolt expansion boxes to the new Mac Pro. Expansion boxes like the ones from Sonnet and OWC let you pull the video input or graphics output card to your Thunderbolt Mac. They can also let you connect multiple eSATA drives to a Thunderbolt Mac if your company has standardized on eSATA drives. Displays aren't a problem either: the system can support up to three 4K displays via Thunderbolt, but you can always connect a single HDMI display to the HDMI port and multiple DVI, VGA, or DisplayPort monitors using adapter cables. Functionally, external expansion can work just fine.

External Expansion Is Messy
External Expansion may work, but it is messy. Anyone who has hooked up an old-school stereo or home theater AV receiver can testify that while using wires to connect components is simple, it also has the potential to breed a rats' nests of wires that can take the patience of a Tibetan monk to unravel. Each new device needs its own cable, sometimes two if you're using a device with a passthrough. Think of it this way: each additional cable further weakens the looks of the minimalist exterior of the Mac Pro. Also, don't forget, businesses like music and movie production use a lot a specialized hardware that may only come on PCIe cards.

Moving an older Mac Pro with internal expansion across the room is currently easy: just unhook the monitor, power, drive cables, and possibly Ethernet, then lift the system over to its destination. With the new Mac Pro, you may need to unhook many more wires from the system, carry the expansion boxes to their destination, and then carry the Mac Pro. The new design is much more of a pain if you have a lot of specialized equipment that doesn't interface directly with Thunderbolt or USB 3.0.

External Expansion Meets/Wastes Bandwidth
If you are using PCIe 2.0 cards in your current Mac Pro, then you should be able to use a Thunderbolt external PCIe chassis and be fine. Each lane of PCIe 2.0 has a theoretical max bandwidth of 4Gbps, well under the theoretical limit of Thunderbolt (10Gbps per channel). Each Thunderbolt controller has 4 lanes of PCIe 2.0 (PCIe x4), totaling to about 16Gbps. The Thunderbolt controller takes half of that bandwidth for each port and puts it on the Thunderbolt 10GBps serial channel. The issue is when you start talking about PCIe 3.0 and later, which tops out at 8Gbps per lane. Hook up one high-end video capture card, and you're potentially oversaturating the Thunderbolt interface. Thunderbolt 2-certified expansion boxes (20Gbps per serial channel) will help later, but for the time being Thunderbolt 2 devices are scarcer than Mac Pros. Sure most consumers won't ever need this kind of power, but the users that buy Mac Pros most certainly have that potential. They're certainly going to be vocal if the expensive expansion cards they've come to rely on don't perform as expected.

Is It Worth It?
If you are planning to move your Mac Pro often, you better hope that one or two external devices plus the dual FirePro GPUs and Xeon processor are enough to do your work. In that case you'll be procuring a much better setup with a small form factor workstation that can easily be moved around an office or from building to building.

However, if your current Mac Pro has all four PCIe card slots filled along with the four hard drive bays, the situation becomes a bit direr. A new Mac Pro setup under those circumstances will involve multiple expansion boxes, many cables, and potentially multiple power plugs as well. In that case, the potential to jump ship and buy an alternative Windows-based expandable workstation becomes that much more attractive.

We'll reserve our final judgment when we get the new Mac Pro on our lab bench later this fall, but until then, follow PCMag.com for more on the new Macs from Cupertino.