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What is the meaning of full-width link and half-width link in peripheral specifications of CPU/microprocessors?

I am studying the bus characteristics of microprocessors for a seminar that is part of a course of computing system foundations that I am taking at the university. I am studying Intel Itanium. In this website I found the following description (I am just showing the part I am interested in) about one of the processors in this family:

Intel Itanium 2 9310

Integrated Peripherals and Components:
Other Peripherals:

  1. Two DDR3 memory controllers
  2. Quick Path Interconnect with 4 full-width and 2 half-width links

I read a bit about Quick Path Interconnect, but I was not able to discover the meaning of full-width and half-width links.

Can anyone tell me what full-width and half-width links mean in this context?
Thanks in advance.