V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

GTL
       Gunning Tranceiver Logic+ [bus] (Intel, SMP), "GTL+"


The Free On-line Dictionary of Computing (30 December 2018):

Gunning Transceiver Logic
GTL

    (GTL) A
   standard for electrical signals in CMOS circuits used to
   provide higher data transfer speeds with smaller voltage
   swings [compared with what?].

   The GTL signal swings between 0.4 volts and 1.2 volts with a
   reference voltage of about 0.8 volts.  Only a small deviation
   of 0.4 volts (or thereabouts) from the reference voltage is
   required to switch between on and off states.  Therefore, a
   GTL signal is said to be a low voltage swing logic signal.

   Gunning Transceiver Logic has several advantages.  The
   resistive termination of a GTL signal provides a clean
   signalling environment [what?].  Moreover, the low terminating
   voltage of 1.2 volts results in reduced voltage drops across
   the resistive elements.  GTL has low power dissipation and can
   operate at high frequency and causes less electromagnetic
   interference (EMI).

   GTL/BTL: A Low-Swing Solution for High-Speed Digital Logic
   (http://edtn.com/scribe/reference/appnotes/md003ecc.htm).

   (2000-01-16)