3-pipes is a feature that allows users to have 3 Monitors plugged in. It is present at 3rd Generation Intel® Core™ processors with Intel® HD Graphics (codenamed IvyBridge) and 4th Generation Intel® Core™ processors with Intel® HD Graphics (codenamed Haswell).

For other platforms only Dual outputs are supported.

IvyBridge limitations

In order to get 3 screen outputs at Ivybridge you shall use 2 Display Ports + any display with some limitations on modes supported.

Easy way to verify what modes are supported is using this script.

Haswell limitations

Haswell 3-pipes is less restrictive than Ivybridge. You can have 3 screns with

* 2 Display Ports + any display

* 1 Display Port and 2 HDMI or DVI

* 1 VGA and  2 HDMI or DVI

and no restrictions on mode combination.