Difference between Spectre, SpectreS, HspiceS, HspiceD

Well, hspice is a circuit simulator from Synopsys; spectre is a circuit simulator from Cadence. There are obviously lots of differences - and clearly I would be biased towards spectre ;-)

For each simulator, there are two interfaces. There is hspiceD and hspiceS (hspice Direct, and hspice Socket), and
spectre and spectreS (spectre direct, and spectre Socket).

The "Socket" interfaces are the obsolete interfaces to the simulators. In the past, many simulators did not have a strong parameterisable language, and so what the Cadence tools did was use cdsSpice (which had a strong macro language, but was a fairly weak simulator) to act as a front end to the end simulator. All netlists were created in cdsSpice's macro language, and then translated into the destination simulator's language - without any parameterisation remaining.

Such an approach worked, but it tended to mean that you couldn't access all the features of the underlying simulator.

A few years ago (back in IC443, around 1999), the "direct" interfaces were introduced, and we're now cutting out the middle man and directly netlisting the right language. This is faster, more efficient, and gives greater access to the underlying simulator.

So the hspiceD and spectre interfaces are the ones to go for. Which simulator you pick depends on your needs.

Regards,

Andrew.