On the front side of the XD-Picture card to the left of the number of Mega Bytes will be no marking or an M or an H.
512MB, M512MB, H512MB. The OLYMPUS D-395 Digital Camera I
have will only take the non M or H type (512MB). This is what I found, hope it helps
The Type M was released in 2005. It uses Multi Level Cell (MLC) architecture to achieve higher storage capacity than the 512MB. Although Type M capacity will eventually stretch to 8GB, the 1GB card is currently the only card in this range. The Type M suffers some compatibility issues with older cameras (especially video recording) and marginally slower readwrite speeds than the 512MB card. More recently Type H cards were introduced which do not seem to offer significant speed improvements | 