they are called flash memory of different format.

micro SD is the smallest form of SD card originally developed by sandisk and few other makers whereas m2 is the smallest form of memory stick by Sony.

historically, SD was made to compete with sony MS.

and nowadays, different device use different format. e.g. SE phones use mostly sony memory stick whereas nokia, samsung and few more adopt the SD format. weirdly enough, SE k850i can take both m2 and microSD.

in term of size, micro sd is slightly smaller than m2. in term of usability, micro sd is more widely used, m2 and ms is usually retained in sony devices only.

dont think so. Sony will not ditch that. people going for Sony devices, have no choice but to use their own memory card.

but i would go for microSD too, it is very universal for a lot of devices.