@inder, Unlike previous PSP models, the PSP Go does not feature a UMD drive, but instead has 16GB of internal flash memory to store games, video, and other media. This can be extended by up to 32GB with the use of a Memory Stick Micro (M2) flash card. Also unlike previous PSP models, the PSP Go's rechargeable battery is not removable or replaceable by the user. The unit is lighter and smaller than the original PSP. The screen slides up to reveal the main controls. Hope this helps...
PS: The Universal Media Disc (UMD) is an optical disc medium developed by Sony for use on the PlayStation Portable. It can hold up to 1.8 gigabytes of data. It is the first optical disc format to be used for a handheld video game system.