Display Port Monitors with MacPro 2013

just follow the instructions for using three displays per 5770. you will of course block another PCI slot and only have 4x (mabe 8x) on the 2nd 5770.

Apple Mini DisplayPort adapters: Frequently asked questions (FAQ)

http://support.apple.com/kb/HT3382

Guide to Apple graphic display adapters needed
https://support.apple.com/kb/HT3235

https://support.apple.com/kb/HT3235
Atlona (Dual Link) DVI to Mini DisplayPort Converter for Apple 27-inch LED and 27-inch iMac

http://www.atlona.com/Atlona-Dual-Link-DVI-to-Mini-DisplayPort-Converter-USB-Pow ered.html

1.

we can connect up to 6 monitors with mini-display port ... it does not mention Display Port models, that can be connected via a Display / Mini Display port adapter.

DisplayPort is electrically the same as Mini DisplayPort. The adapter is simply a re-assignment of the pins to the different connectors. Some users find this adaptation is better performed with an adapter-cable, rather than a discrete adapter. Rules that apply to Mini DisplayPort stand exactly the same as (full size) DisplayPort.

2.

connect 2 monitors with DVI to Mini DP adapters AND 2/3 monitors with Display to Mini DP adapters at the same time ?

These appear to be limited to 2 Single-Link DVI adapters unless you use USB-powered ACTIVE adapters. This setup is complicated, and that is not "The Apple way". it may suddenly require ALL adapters be ACTIVE adapters.

3.

VGA to Mini DP adapters : does that mean that I can use 5/6 monitors at the same time that way ?

No. These will also be limited to easy use with the two display adapters. In today's digital display age, VGA is not a solution to anything. It is grudgingly provided to run your old projector.

All VGA Adapters are ACTIVE -- they contain a chip that generates the Analog signal from the DisplayPort signal provided, and the VGA signal degenerates further in the process, and has limited resolution. There are no VGA Adapters which have the extra USB input, so that alone may limit you to the two specified.

4.

For completeness, keep in mind that a 4K display can use up to 14G bits/second (variable depending on how much is changing on screen) for a moving picture, so there may not be as much as expected left over on that 20G bits/sec ThunderBolt channel (2 ports/channel) to run your Drives.

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2. additional clarification:

I am sure two adapters to Single-Link DVI will work fine.

I expect you can mix in additional [Mini] DisplayPort cables for up to six displays.

What we do not yet know for sure is 'pressing on beyond two DVI displays'. It is not specifically precluded by that article, but it could get really complicated, with lots of expensive adapters that need additional (USB or equivalent) power.

That is normal. One card is doing calcualtions while the other is doing the displays.

Are you runing 10.9.3?