The S750 Uses custom expander board Roland part # RAS750 and 30 pin SIMM470 @ 100ns. Unit has 2Mb stock (soldered on logic board); then you must install an RAS750 before you can install SIMMs. 4 memory slots total on RAS750 can be updated to 18Mb via (4) SIMM470 and the 2Mb on logic board. SIMMs must be installed in groups of four.