128Mbit technoloy RAM versus 64Mbit technology RAM

How do I dentify the difference between 64 and 128 Mbit technology?
(The pdf files I downloaded for the MS6188 motherboards I’m actually building into PIII sets tells me that they can take 256 (2 x 128) on 64 Mbit tech and 512 (2 x 256) on 128 Mbit tech. I would like to upgrade to 512 but do not know how to identify which module to use

In what way is PC100, PC133, PC333 etc related to 64 Mbit technology and or 128 Mbit technology?
Is for instance an 256 SDRAM PC133 333 stick necessarily 128 Mbit technology?
Then there’s PC133L and PC133U – all very confusing
Enlighten me please!