The K2000S and K2000RS use 30 pin SIMM1, SIMM470, SIMM8C, SIMM8J (J or C depends on type of mother board), or SIMM16 @ 80ns or faster. 2Mb stock, unit has (4) SIMM sockets total. Can be upgraded to 64Mb via (4) SIMM16s. SIMMs must be installed in pairs. You can mix SIMMs as long as they are installed in matched pairs (ie two SIMM4 and two SIMM16). SIMMs should be installed into the outer sockets first and then the inner sockets (larger SIMMs should be in the outer sockets).