From Past Experience: and 3 days loss of data trying to restore: If your new mac pro has come factory fitted with Yosemite, Do NOT try and downgrade to Mavericks. You will read a lot on the net about some chancer who 'successfully' managed to downgrade their nMP from Yosemite to Mavericks - by booting up from a second disk/thunderbolt tether, and formatting the internal SSD then insttalling Mavericks from USB stick. Don't ********ing try it ! As i found out (the hard way) there are certain internal hardware drivers and firmware motherboard support specifically designed onlyto be read by Yosemite. You go messing around back-grading to Mavericks, and it may work initially, but you will see regular failures, errors and system crashes - particularly trying to load some legacy software. I even put a brand new OWC Aura 2TB internal SSD into my mac, freshly formatted, and tried to install Mavericks from a USB bootable flash drive. At first it worked, Mavericks was up and running. Then crashed when trying to render After Effects (gave some D500 graphics error), then it wouldn't boot, then tried to re-install Mavericks, it hung...and it hung for about 3 days - stuck in limbo. I thoguht for a moment i REALLY was left with a £4,000 Trashcan ! Eventually i managed to take the SSD out, freshly format it as factory new, and install a fresh clean version of Yosemite in it. All is fine now. Your New Mac Pro is a clean, modern and bang-up to date to workstation, with precicely engineered high performance hardware that integrates perfectly with Yosemite. Don't go ****ing with this ! If it ain't broke, don't try and [break] it. Don't go ****ing with the programme !