yes its a memory card a smaller version
microSD, microSDHC, and microSDXC.
The most expensive Panasonic SD memory card is the 64GB SDHC Memory Card and the most expensive Panasonic MicroSD memory card is the 32GB MicroSD memory card.
MicroSD with Up to 4GB of memory max.
The microSD memory card slot supports up to 16GB
TransFlash Card
It reads the microSD, Memory Stick Micro (M2), microSD High Capacity (microSDHC) - USB memory cards.
The SanDisk 8 GB MicroSD card has more than enough memory for a PSP, which only needs about 2 GB.
please, tell me how i can erase my microsd memory card's password
The R4 doesn't hold memory, it's the MicroSD card that you insert into the R4DS that has storage. It will support MicroSD cards with storage of up to 2GB (non-SDHC).
Micro SDHC
trans flash
It means that your R4 is not able to correctly read your microsd memory card. Remove it and re-insert it a couple of times from your R4. If it doesn't work try re-formating your microsd memory card