What is the “dual” in DIMM?

DIMM is an acronym for Dual Inline Memory Module. To what does the “dual” part of a DIMM refer?

A) The electrical contacts on a DIMM are different on each side

B) DIMMs are twice the size of SIMMs

C) DIMMs must be installed in pairs

D) Memory chips are installed on both sides of a DIMM

E) DIMM memory modules have really bad mood swings