difference between type I and type II compact flash?

What is the difference, is it speed, and if so by how much?
Many thanks

Here.
I think that recent cards based on solid state memory are all Type I.

I've never actually seen a type II (thicker) CF card advertised: has anyone?

'CFII compatible ' has really just become a way of manufacturers saying their camera will take Microdrives without having to use the (trademarked?) word 'Microdrive'.

There were old (if I remember right they were 64MB) Canon cards which were type II. But that was a while ago Nowadays only cards which are type II are Microdrives (if they still exist).

Type 1 are 3.3 mm thick; Type 2 are 5 mm thick. Not to be confused with SanDisk's Ultra II, Extreme III and the like which are model numbers, not specifications. Type 2 CF was used for larger-capacity CF cards when memory chips hadn't reached the current capacities, and for some CF IO cards, such as wireless, digital cameras and the like.