PGS - "Pure Gold Signal": a single, very thin (0.004" in diameter), 99.99% pure gold signal conductor, surrounded by porous Teflon® insulation, and a complex cross-wrapped "return" (multiple thin strands).
PGS was beta-tested in 1999 and was in production since December 1999 until April 2002 (when it was replaced with the PGS-XL).
After several years in production and several hundred opinions collected, it became clear that the PGS is one of the most "refined" and "analog sounding" interconnect cables in existence. Note - the same as with copper and silver cables, not all gold cables sound the same! There is much more than just using pure gold wire in these cables.