XD-Picture Card

xD-Picture

A 16 MB Fujifilm xD Card
Media type	memory card
Capacity	maximum 512 MB (original) maximum 8 GB (Type M and Type H)
Developed by	Olympus, Fujifilm
Dimensions	20 mm × 25 mm × 1.78 mm
Weight	2.8 grams
Usage	digital cameras, voice recorders

The xD-Picture Card is a type of flash memory card, used mainly in digital cameras. xD originally stood for extreme Digital. The cards were developed by Olympus and Fujifilm and introduced into the market in July 2002. Toshiba Corporation and Samsung Electronics manufacture the cards for Olympus and Fujifilm. xD cards are now sold under other brands, including Kodak, SanDisk, and Lexar.

xD cards are used in Olympus and Fujifilm digital cameras and Olympus digital voice recorders; Fujifilm also made an MP3 player that used the cards. As of 2006, xD cards are available in capacities of 16 MB, 32 MB, 64 MB, 128 MB, 256 MB, 512 MB, 1 GB, and 2 GB. xD cards have dimensions of 20 mm × 25 mm × 1.78 mm, and each weighs 2.8 grams.

Type M and Type H cards

xD-Picture Card, 1G, type M

The original xD cards were available in 16 MB to 512 MB capacities. The Type M card, released in February 2005, 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.

xD-Picture Card, 512M, type H

The Type H card, first released in November 2005, offers higher data rates than Type M cards (theoretically as much as 3 times faster). As of 2006, Type H cards are only available in 256 MB, 512 MB, 1 GB, and 2 GB capacities, with 2 GB cards being sold in Japan before the rest of the world. Olympus says that its Type H xD cards support special "picture effects" when used in some Olympus cameras, though these software features are not intrinsically hardware-dependent. This dependence may be seen as a weak form of tying. However type H cards are required in newer models to capture video at high rate (640x480x30).

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.

Theoretical transfer speeds

Pictures may be transferred from a digital camera's xD card to a personal computer by plugging the camera into the PC (via a USB cable), or by removing the card from the camera and inserting it into a card reader. In both cases, the computer sees the card as a mass storage device containing image files, although software or firmware can alter this representation. Card readers may be integrated into the PC or attached by cable. Adapters are available to allow an xD picture card to be plugged into other readers (and in some cases cameras), including PC card, parallel port, CompactFlash and SmartMedia.

Type	Capacity	Write speed (MB/s)	Read speed (MB/s)
Standard	16 MB, 32 MB	1.3	5
	64 MB, 128 MB, 256 MB, 512 MB	3	5
M	256 MB, 512 MB, 1 GB, 2 GB	2.5	4
H	256 MB, 512 MB, 1 GB, 2 GB	4	5

Comparison with rival formats

The xD format primarily competes with formats such as Secure Digital card (SD), CompactFlash (CF), and Sony's Memory Stick.

Advantages

• xD cards are fast in comparison with older formats such as SmartMedia (SM), MultiMediaCard (MMC), and MemoryStick (MS).
• xD cards have a small form-factor in comparison with other formats (although both Micro SD and Memory Stick M2 are smaller).
• xD cards have a low power consumption.

Disadvantages

• Traditional xD cards have a fairly small theoretical maximum capacity, relative to other memory card formats. The newer Type M and H variants have addressed this issue, with a maximum capacity of 8 GB.
• xD cards are much slower than their main competitor, SecureDigital (SD).
• Although xD cards are smaller than, for example, SecureDigital (SD) cards, they are larger than some of the newer small-factor versions, such as miniSD and microSD cards.
• xD cards are generally more expensive than cards of other formats.
• xD cards are less widely supported by camera, card reader, and accessory manufacturers than CompactFlash (the de facto standard for professional and prosumer digital cameras) and SD (supported by many brands of digital cameras, MP3 players, and other portable devices).
• the xD card format is proprietary to Fujifilm and Olympus, just as the Memory Stick format is to Sony. This means that no public documentation or implementation is available (see below for reverse-engineering results). By comparison, the MultiMediaCard and CompactFlash formats are described by completely open and free specifications, and a partial specification for the SD format is freely available.

Detailed specifications

The detailed specification for xD cards is tightly controlled by Olympus and Fujifilm, which charge licensing fees and royalties and require non-disclosure agreements in exchange for the technical information required to produce xD-compatible devices.

The memory format used by xD cards is not well-documented. It is difficult to study it directly, since most camera devices and most USB card readers do not provide direct access to the flash memory. Since the cards are controller-less, cameras and card readers must perform wear leveling and error detection themselves, and they normally hide the portion of the memory which stores this information (among other things) from higher-level access.

However, a few models of xD card readers based on the Alauda chip do allow "raw" access to an xD card's flash memory; these readers have been reverse-engineered and Linux drivers have been produced by the Alauda Project, which has also documented the on-chip data structures of the xD card. According to this information, the xD card headers are similar to those used by SmartMedia, and include information on the manufacturer of the chip.

Raw hardware

The back of an xD card, showing the 18 pins

At the raw hardware level, an xD card is simply an ordinary NAND flash integrated circuits in an unusual package. Comparing the pinout of an xD card to the pinout of a NAND flash chip in a standard TSOP package, one finds a nearly one-to-one correspondence between the active pins of the two devices. xD cards share this characteristic with the older SmartMedia cards, which are also basically raw NAND flash chips, albeit in a larger package.

xD cards and SmartMedia cards can be used by hobbyists as a convenient source of NAND flash memory chips for custom projects. For example, the Mattel Juice Box PMP can be booted into Linux using a modified cartridge containing an xD card with the boot image written to it. Additionally, SmartMedia and xD card readers can be used to read the data off of NAND flash chips in electronic devices, by soldering leads between the chip and the card reader.

Panoramic mode

Olympus-branded xD cards are the only ones that support Olympus cameras' panoramic function. Although they store data identically to other manufacturers' cards, Olympus intentionally disables this feature in the hopes that buyers will purchase their cards (a form of vendor lock-in).

However, it appears that the card manufacturer information is simply stored in the flash memory, in the Card Information Structure (described in the Alauda Project's documentation, see above). Thus, it is possible to alter another brand of xD card to present itself as Olympus xD card by accessing the raw flash memory.

Market acceptance

Because of their higher cost and limited usage in products other than digital cameras as of 2005, xD has been losing ground to SD, which is broadly used by PDAs, digital audio players, and most other digital camera manufacturers.

It is perhaps surprising that xD cards cost more than SD cards, since SD cards must contain a controller circuit in addition to the NAND flash memory. However, SD cards are produced in much greater numbers and by more manufacturers, so economies of scale and increased competition probably explain the significant price disparity.

While many Olympus and Fujifilm digital cameras use xD cards exclusively, a limited number—such as the Olympus E-500, the Fujifilm S7000, and the Fujifilm S9500—can access other memory card formats, such as CompactFlash, in addition to xD. Recent Fujifilm cameras like the FinePix: A610, A800, A805, S5700, S8000, and F40fd have card slots that can also utilize SD cards aside from XD.

See also

• Comparison of memory cards

External links

• Licensors' Official Site (Olympus and Fujifilm)