there are several differerent memory sticks.
Original: up to 128 MB
Magic gate: up to 128MB, DRM stuff added to the original
select: 2x128 MB = 256, you select which 128MB block you want to use with a switch on the stick
DUO: up to 128 MB, smaller version of the original, has optional adapter to make it the size of the original
PRO+magic gate: 256-1GB (sandisk has a 2 GB), same size as original
DUO PRO + magic gate: up to 1 GB, same size as DUO but in the PRO spec
notes:
original works in all devices except those which require DUO for size reasons
magic gate works in most devices (there are issues with this)
select works in all devices since it is essentially 2 original sticks in one package (see above)
DUO works in all devices, adapter may be required for those with an original sized slot
PRO+magic gate, only works in the latest sony products due to timing changes relative to the original
DUO PRO+ magic gate, only works in the latest sony products due to timing changes relative to the original, adapter may be required for those with an original sized slot.