DDR2 max number of slots, max Rank

Hi All,

for both Registered and unbuffered DDR2-400 can anyone tell me:

1. the max number of slots for a single controller with only one copy of address /Cmd etc. (1T or 2T address/command clocking)

2. the maximum rank allowed in a system configured as above.

3. if my controller was configured to have two copies of Address and command can I douple up the number of slots and Rank over the configuration in 1 above?

Are registered modules always of the 72bit wide flovour for ECC?

I'm assuming that the protocols between Unbuffered and Registeded modules are the same (maybe Registered has more latency etc) but can anyone highlight any differences in implementation I need to consider (pinouts seem to be different).

Many thanks.