A SIMM differing from a DIMM may be installed in a mainboard in a bank consisting of two memory modules, compared to the standard single DIMM. These predate DIMMs and are not at large, nor fast, but are the beginning to upgradable RAM modules. To install, place in socket at an angle and rotate into position. To remove, pull metal clips to the side and rotate out and pull up. They are not as user friendly as a DIMM.