This Mac Pro has been used almost exclusively for audio recording/playback. It has been tested and re-installed with Mac OSX 10.11.6 El Capitan. Only one of the drive bays is occupied with a 1TB HDD. 
 
Specs:
2.8GHz Quad Core Intel Xeon processor
16GB RAM
ATI Radeon HD 5770 1024MB graphics card
4 internal 3.5" SATA bays
4 PCIe 2.0 slots
5 USB 2.0 ports
4 Firewire 800 ports
Dual Gigabit Ethernet
2 Mini DisplayPorts
1 Dual-link DVI port
AirPort Extreme (802.11 a/b/g/n)
Bluetooth 2.1+EDR