Hi there, that would depend on the age of the system aswell as the make of the mobo... SIMMs where used on old P I and AMD K5/K6 boards and there was a change there after/along to DIMMs... I would suggest that you post the model and age of the system as that would help point down what type of MEM you use... you could call DELL and ask them this very same question, or take out you existing RAM Module and with it could go to a local PC store and have them give you a larger stick or such...
Ben