Type M/M+ and Type H cards
The original xD cards were available in 16 MB to 512 MB capacities. The Type M card, released in February 2005[2], uses Multi Level Cell (MLC) architecture to achieve a theoretical storage capacity of up to 8 GB. As of August 2006, Type M cards are available in sizes from 256 MB to 2 GB. However, the Type M suffers slower read-write speeds than the original cards.
The Type H card, first released in November 2005[3], offers higher data rates than Type M cards (theoretically as much as 3 times faster). As of 2008, Type H cards are only available in 256 MB, 512 MB, 1 GB, and 2 GB capacities.
The Type M+ card, first released in April 2008[4], offers data rates "1.5 times" that of Type M cards. As of 2008, cards are available only in 1 and 2 GB capacities.
Olympus says that its xD cards support special "picture effects" when used in some Olympus cameras, though these software features are not intrinsically hardware-dependent. Type H and M+ cards however, are required in newer models to capture video at high rate (640×480×30). Due to changes in the cards' storage architecture, newer Type M and H cards may suffer compatibility issues with some older cameras (especially video recording). Compatibility lists are available for Olympus: Olympus America’s and Fujifilm’s. The newer cards are also incompatible with some card readers.