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.

The Memory Stick Duo can always be used in a Memory Stick PRO Duo slot and in most of the cases a PRO card can be used in a Memory Stick Duo slot. We recommend you to look in the product’s manual for finding out if a Memory Stick PRO Duo can be used in your product’s Memory Stick Duo slot. However you will not be able to make use of the higher transfer speed that the Memory Stick PRO Duo has to offer when using it on a standard Memory Stick Duo slot. In cases like that the PRO card will have the same transfer speed as a standard Memory Stick Duo.

All Memory Stick Duo and Memory Stick PRO Duo cards always come with a Memory Stick or a Memory Stick PRO adaptor making them compatible to all Memory Stick slots. The Memory Stick Duo and Memory Stick PRO Duo can be found branded only under the name of Sony, SanDisk and Lexar. The Memory Stick Duo and PRO are almost exclusively employed by Sony and SonyEricsson products, mostly by SonyEricsson’s mobile phones and Sony’s PlayStation Portable, PSP.

The write protection switch on the back side of the card is not a standard feature on all Memory Stick Duo and Memory Stick PRO Duo cards.