Dedicated circuitry on supported device(Arria series, Cyclone IV, Stratix IV GT, and Stratix IV GX) family devices that uses differential I/O standards and Clock Data Recovery (CDR) to send and receive data serially at a faster rate between devices.
This dedicated CDR circuitry enables supported device family devices to eliminate frequency barriers faced by source-synchronous systems, allowing for data transmission while correcting for clock skew.
You can take advantage of the GXB with the ALTGX megafunction.