how many pins does a DIMM have?

Answer 1

168 pins for standard PC memory
144 pins for laptop memory
100 pins for printer memory

Answer 2

Well... It depends on what kind of DIMM you are asking about.

In desktops:

SDRAM one of the first to be DIMM has 168

DDR has 184

RDRAM had 184 as well though with different notches in the stick.

DDR2 has 240 pins.

Laptops had 144 for SDRAM SoDIMMs and 200 pins for DDR and DDR2.