Memory Stick Duo was introduced in 2003 by Sony Corporation as the second form factor memory card in the Memory Stick family. It is a smaller alternative to the Memory Stick and was developed to be used in small portable electronic devices, mostly mobile phones. It has the size of a postage stamp and has about half the volume of a Memory Stick.
The limitations of the Memory Stick Duo in storage capacity, max 128 MB, and transfer speed, 2.45 MB/sec, contributed to the introduction of the Memory Stick PRO Duo, later in 2003. The PRO platform was developed jointly by Sony Corporation and SanDisk Corporation. It has the same physical format as the standard Memory Stick Duo but the PRO platform offers higher storage capacity and higher transfer speed.