PC133 and PC100 compatibility

Hi Guys......

I have some questions to ask, I had my headache because of it :slant:

I Just bought a RAM for a couple of weeks ago

RAM Specs:

Apacer 256MB UNB PC133 CL3 SODIMM

I know it's kind a stupid, but in short... I need a RAM for my Laptop(Satellite 2805), it uses PC100 RAM 128MB and I want to switch it with 256MB,

so I bought one from ebay (it`s cheaper), but as I tried it,

the memory amount displayed without any error but I couldn't boot into my Operating System.

My Question are

What kind of error do I have ? I can't really figure it out because I read that PC133 SHOULD be compatible with PC100

What is the meanig of CL and UNB ?

I know it's a boring questions, but Thanks for all of your help..

First of all, define "but I couldn't boot into my Operating System."