Difference between spectre, spectreS, Hspice, HspiceS

there are two simulation "methodes" in cadence dfII:
1. direct simulation approach, spectre, HspiceD,
2. socket simulation approach, spectreS, HspiceS

the direct simulation approach is more efficient than the socket simulations, because there the netlist have to be translated first into a cds-spice netlist.

spectreS stands for spectre in Spice-Socket. So the netlist is similar to spice. In the analog artist the components are netlisted as Spice primitives where most simulator commands are in spectre native language. Spectre themselve differentiate between spectre native syntax and Spice syntax with a language switch command.

The socket comes from old cadence spice called cdsSpice.
All the third party simulators can be integrated to cadence using this cdsSpice socket(example hspiceS, eldo etc smartSpice mica tispice).

Cadence Artist <=> cdsSpice <=> Thirdparty simulators

However, this is kind of obsolete now.
Cadence now promotes Direct Simulation Interface(OASIS) for third party vendors. So no more socketing. For example,
The hspiceS will become hspiceD but the simulator is still the same.
Bottomline it is all about the netlisting but the simulator is just the same.

Quated from http://www.edaboard.com/ftopic74615.html