"TDK's development comes hot on the heels of an announcement by Toshiba that it has developed a three-layer HD-DVD disc capable of holding up to 45GB of information. HD-DVD is a competing format to Blu-ray Disc and HD-DVD's maximum capacity of 30GB had been viewed unfavorably against Blu-ray Disc's maximum 50GB capacity.
According to the Blu-ray Disc Association, a single-layer 25GB disc can typically hold 135 minutes of high-definition video in MPEG-2 format, with room for a further two hours of standard-definition video.
The recent Toshiba announcement brought the formats much closer together and made capacity less of an issue for the Blu-ray Disc camp to trumpet when promoting their technology. The development of a 100GB disc by TDK will likely open up this avenue for the Blu-ray Disc supporters again."
I believe this makes 3 players in the High Def Disc market. Sony, Toshiba and now TDK.