It has a voltage swing between 0.4 volts and 1.2 volts — much lower than that used in TTL and CMOS logic — and symmetrical parallel resistive termination.
GTL is defined by JEDEC standard JESD 8-3 (1993) and was invented by William Gunning while working for Xerox at the Palo Alto Research Center.
As of 2008, GTL in these FSBs has a maximum frequency of 1.6 GHz.
[1] The front-side bus of the Intel Pentium Pro, Pentium II and Pentium III microprocessors uses GTL+ (or GTLP) developed by Fairchild Semiconductor, an upgraded version of GTL which has defined slew rates and higher voltage levels.
These are GTL signaling derivatives used by Intel microprocessors.