Types of GM ECMs

[bruce plecan]

As far as series types of ecm for GM;
As I understand it there are C3, P4, and PCMs.  Is this true?

All the C3 types use a 2732 style prom, and 2 connectors.

All the P4 use a memcal/calpak, use 27128/27256 proms, 
and 3 connectors.

What do the PCMs use?.

Are there other GM EFI series?.  Is the prom holder/memcal.
connector an accurate way of id ing them?..
Bruce    Beginning to wear two cone shaped hats, one
             inside the other.  Now have 4 layers of AL foil to 
             block alein tranmissions...