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The Institute of Environmental Sciences and Technology (IEST) has information on their website regarding ISO 14644-1. Their website is www.iest.org.
A PSX ISO would probably refer to an ISO image made from a PlayStation 1 CD.
In August 2016 the rating was moved from ISO 2 to ISO 1- best there is!
Abe Iso was born on March 1, 1865.