[quote="Frank Wegener"]Kleine Frage an die Experten: enthalten sind zwei engines:
eine "normale" (1,1 MB) sowie eine "popcnt"-Version (etwa 250 kB).
Was gibt es da für Unterschiede?[/quote]

The only difference is how a certain low-level computation is done: Many places in the evaluation function, Stockfish needs to count the number of squares in some set of squares. For instance, when computing the mobility of a piece, Stockfish first finds the set of squares the piece attacks, and then counts the number of squares in this set. When evaluating king safety, it finds the set of squares close to the king which are attacked by enemy pieces, and counts then number of squares.

The "popcnt" version uses a hardware instruction to do this counting operation. The normal version uses a somewhat slower software approach. Unfortunately, the hardware instruction is only available on the most recent Intel CPUs, that's why we provide two versions.

If you are not sure whether your CPU supports the "popcnt" instruction, just try running the "stockfish-popcnt" binary. If it works, use that one, as it is a little faster (around 5%, if I recall correctly) than the normal version. If it doesn't work, you have an older CPU, and must use the normal version. Apart from the slight difference in speed, the two versions are identical.