My question is about the MacPro (old model).

Mac Pro 2012(2011 as well?) or later I guess.

The 2010 Mac Pro initially came with Snow Leopard on DVD and that was the last Mac OS X being made available on DVD. Later 2010 Mac Pro's came with Lion, which was download only. The 2012 Mac Pros first came with Lion and later Mountain Lion, both of which are download only.

Of course, you can make your own USB flash drive into a DVD equivalent using the downloaded installer, boot from it, and install your OS that way.

What is really interesting is that without the ability to do one of:

• Boot from a DVD

• Have Internet Recovery in the firmware, not just in Recovery_HD

These Macs are one drive failure away from not being able to restore their software at all.

Any owner of these Macs should have a 1GB USB thumb drive with a copy of Recovery_HD (made using Recovery Disk Assistant) taped to the side. It is created by copying your installed Recovery_HD onto the USB stick, so you cannot make it later if your boot drive fails and you have no clones.

And even if you do have Internet Recovery ability (and what if the net is having trouble?) or you want to reinstall: If you wanted the 10.9.2 installer, and maybe only 10.9.3+ is now offerred...

... If you clone your system (before making change or update or whatever or just to do so) then Carbon Copy Cloner will also put Recovery on the other drive. hopefully you are already using and know how to use CCC.

no need to or have to have a flash drive, you can or you can put it anywhere else too.

A full installer package generally requires a 16GB volume, flash is fine but slow, you can put it on USB or Firewire or on create a small partition on your TimeMachine drive. Doesn't matter.

Instructions on how to: