Just adding, that there is also option "E" in these FAS32xx series.
FAS3240 = Single head, with 2 expansion slots
FAS3240E = Single head, with 6 expansion slots.
FAS3240A = 2 controllers in two different chassis, including 2 expansion slots/chassis
FAS3240AE = 2 controllers in two different chassis, including 6 expansion slots/chassis.
E = I/O Expansion module (4 slots)
A = active-active
HA = high availability
A = HA