The Memory Stick Duo was developed in response to Sony's need for a smaller flash memory card for pocket-sized digital cameras and cell phones. It is slightly smaller than the competing Secure Digital (SD) . The Memory Stick PRO Duo quickly replaced the Memory Stick Duo due to its size limitation of 128MB and slow transfer speed. In March 2008, Sony released a 16GB version of the Memory Stick PRO Duo. Sony has plans to release a 32GB version in 2009. Theory says though that the theoretical maximum could be 2TB, equal to the SDHC limit.