Pentium II , Part numbers at a glance.

Here's a quick list of how to figure out part numbers. I left out the pentium mmx stuff because it's almost gone anyway.

pentium ii / klamath / 66MHz FSB
80522PX233512 = 233mhz
80522PX233512EC = 233mhz w/ ECC
80522PX266512 = 266mhz
80522PX266512EC = 266mhz w/ ECC
80522PX300512EC = 300mhz (only offered w/ ECC)

pentium ii / deschutes / 66MHz FSB
80523PX300512PE = 300mhz
80523PX333512PE = 333mhz
("PE" designator at the end means updated tag SRAM--allows dual processing--everything shipping how will have this designator)

pentium ii / deschutes / 100MHz FSB
80523PY350512PE = 350mhz
80523PY400512PE = 400mhz
80523PY450512PE = 450mhz

celeron (covington - no L2 cache)
80523RX266000 = 266mhz
80523RX300000 = 300mhz

celeron (mendocino - 128k L2 cache)
80524RX300128 = 300mhz (designated as 300A Mhz)