PC133 is an open standard for
SDRAM memory, building on
Intel's PC100 standard. The
architecture of the two are as good as identical, the main difference being the differing
clock speeds: respectively 133 and 100
MHz.
The PC133 standard is developed by JEDEC (www.jedec.org), helped by VIA, Micron, NEC and Samsung (among others).
Thanks to justabot for additional information.