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Memory Cards

Computers don't have a monopoly on memory. Today's high-tech toys such as MP3 players and digital cameras also need memory for storing their software—the music you play on your MP3 player and the pictures you take with your digital camera.

The requirements for this memory differs from that you install in your computer. Although you want computer memory to be as fast as possible, speed is not as important as permanence for other electronics. You want your music and pictures to always be there when you want them, not subject to the vagaries of your batteries or utility electricity supply. In a word, cameras and MP3 players want nonvolatile memory.

In addition, you want to be able to quickly add to or exchange the contents of the memory in your camera or MP3 player or to interchange blocks of memory. To allow you to make such exchanges quickly and easily, memory-makers have developed a wide array of memory cards. They work like a PC Card designed to the PCMCIA standard (we considered a PC Card as an expansion bus, which it really is, in Chapter 9, "Expansion Buses"). You simply slide them in, and they work. But, thanks to the benefit of more refined technologies and less need to accommodate non-memory devices such as network adapters and modems, memory cards can be smaller. Some, in fact, are hardly bigger than memory chips.

The first two designs, CompactFlash and SmartMedia, came from two different but well-established directions. CompactFlash simply put the PC Card interface on a smaller card. SmartMedia did little more than repackage Flash memory chips. The latest additions to the memory card zoo all add copy management provisions so that music publishers can control what you put on cards and whether (or even how many times) you duplicate copyrighted material.

The question as to which is better often is meaningless. The best card is the one that your camera or music player uses. However, the medium used may influence your choice of camera or player. A device using CompactFlash gives you more storage and versatility, although other cards yield more compact storage.


Sometimes, even a PC Card is too big, so in a quest for miniaturization, the electronics industry, led by Intel, developed a yet-smaller standard. Appropriately called Miniature Card, it was designed as a reduced-size version of a PC Card aimed particularly at memory devices. Although it never caught on, its heir, CompactFlash, has found wide application in digital cameras. Although engineers designed the Miniature Card to be a general-purpose expansion format, one application dominated the minds of designers eyeing the small cards: memory. A variety of electronic devices have a need for compact and removable memory, perhaps the most important of which initially was the digital camera.

Intel developed Miniature Card and released the initial version (logically enough, version 1.0) on February 29, 1996. Envisioned as the perfect memory solution for digital cameras and miniaturized digital audio recorders, Miniature Cards measured less than an inch and a half square but could store up to 64MB using any standard memory technology. The limit was imposed by the bus design, pure PC Card.

In 1994, PC Card maker SanDisk developed a new small card design as CompactFlash. As the name implies, the company aimed the product specifically at accommodating Flash memory in a format small enough to fit into a digital camera that wouldn't require a mule team to transport.

The CompactFlash specification is now governed by the CompactFlash Association (CFA), founded in 1995 by Apple Computer, Canon, Eastman Kodak, Hewlett-Packard, LG Semicon, Matsushita, Motorola, NEC, Polaroid, SanDisk, Seagate, and Seiko Epson. The organization maintains a Web site at www.compactflash.org.

An early promoter of the various PCMCIA specifications, SanDisk patterned the signals used by CompactFlash cards on the PC Card bus design. Logically, the interface conforms to the AT Attachment specifications, and software accesses the memory on the card as if it were a disk drive.

Electrically, CompactFlash cards act much like full-size PC Cards. As a result, each card must include its own control logic and conform to the logical format standards promulgated by PCMCIA. This makes the cards more complex than the competing tiny-card format SmartMedia, discussed next. Although the larger amount of circuitry also adds to the cost of producing the cards, large-scale integration and high volumes hold the potential of minimizing any such handicap. In fact, the prices of the two media are comparable, although the edge usually goes to SmartMedia.

The added complexity of PC Card compatibility has one big benefit. It allows CompactFlash cards to be readily adapted to full-size PC Card slots. The required adapter card need not contain any electronics, thus making it inexpensive. The only need is to make the small card physically fit into a larger socket, rerouting its circuits to fit the larger connector used by the PC Card standard.

Standard CompactFlash cards measure 43 mm (1.7 in) by 36 mm (1.4 in) by 3.3 mm (0.13 in), the same thickness as a PC Card and about one-quarter the size. To increase physical capacity, the CFA has designed a slightly thicker format, designated CompactFlash Type II. At 5 mm thick, the new format conforms to the thickness of Type II CardBus and PC Cards.

Unlike physical disk drives, however, CompactFlash cards can withstand more physical abuse (about 2000 Gs) and wider temperature ranges (-25° C to +75° C for CompactFlash compared to +5° C to +55° C for typical disk drives). The expected life of the medium is in excess of 100 years, with data integrity protected by both built-in dynamic defect management and error correction.

CompactFlash capacities start at 2MB. Currently the largest capacity per card is 512MB. Up to 1GB is available in the same package using a micro hard disk drive. Systems can double the data storage of any card using compression software, although digital cameras use JPEG compression, which ordinarily cannot be further compressed by standard software-compression algorithms.

The CompactFlash design requires dual-voltage operation. All cards are completely compatible with both 5.0- and 3.3-volt systems. Any card will work in any system, regardless of its operating voltage.

Most operating systems support the PCMCIA logical interface used by CompactFlash cards through software drivers. CompactFlash cards can be used with DOS, Windows 95 and 98, OS/2, Apple Macintosh, and most flavors of Unix.


SmartMedia is the pioneering minimal memory format, at one time (but no longer) the thinnest and smallest type of removable Flash memory card. About one-third the size of a PC Card, a SmartMedia chip (there's no better description) measures 45 millimeters (mm) by 37 mm by 0.76 mm. It appears like a monolithic slice of plastic, and that's almost what it is. Its "overmolded" thin package (OMTP) simply encases one or more memory chips with a solid protective outer shell. Two rows of a total of 22 surface contacts provide the necessary connections for an eight-bit interface.

Originally developed under the name Solid-State Floppy Disk Card (SSFDC), a name that still rules over its supporting body's Web site (www.ssfdc.com), its original creator (Toshiba) has trademarked the name SmartMedia for the format. The SmartMedia format is currently used by the makers of many digital cameras, including nearly all Japanese brands as well as Agfa and Apple.

The small size of the SmartMedia cards does not stand in the way of large capacities. Although originally introduced only in sizes from 2MB to 8MB, Toshiba has developed a high-density connection and packaging system to increase the potential storage of the SmartMedia format. Current specifications allow cards storing up to 128MB.

The total capacity of each card is arrayed in blocks of about 16KB, each block comprising 32 pages of 528 bytes each. Because the memory is solid-state, access time is brief, rated at only 7 microseconds. Transferring a bit through the serial interface requires only 50 nanoseconds, an effective clock speed of 20Mbps. In actual operation, transfer speeds of 0.5 to 1.0Mbps can be achieved. Writing is slower—about two milliseconds to erase a 16KB block of memory and 200 microseconds to write it again.

The heart of each SmartMedia card is one or more NAND Flash EEPROM (electrically erasable programmable read-only memory) chips embedded in the plastic shell. The NAND Flash memory technology used by SmartMedia provides fast write and erase functions plus high-speed read with minimal power consumption.

This simple electrical design is key to the low-cost potential of SmartMedia. Despite the name, the cards are not very intelligent. They contain only memory. The controller is in the host. To work in a PC Card slot, an adapter for a SmartMedia card must itself contain a controller. Adapters are consequently more expensive than slot adapters for PC Cards.

The SmartMedia logical data format is based on the AT Attachment and DOS file standards and is compatible with computers running Windows 95, Windows 98, Windows NT, or OS/2 Warp. It also works on Apple Macintosh computers.

Both 5.0-volt and 3.3-volt cards are permitted under the SmartMedia specification. A notch codes the voltage used by each card to prevent you from putting a board in a host supplying the wrong voltage. A right notch indicates 3.3-volt cards; a left notch, 5.0-volts cards.

The SmartMedia standards are administered through the SSFDC Forum, which you can access on the Web at www.ssfdc.or.jp/english/.

Memory Stick

Sony Corporation developed the Memory Stick package as a proprietary technology. Sony uses Memory Stick as a cross-platform package. The same stick fits digital cameras, digital video recorders, and MP3 players.

Memory Sticks resemble an old-fashioned stick of chewing gum, about 2 inches long (50 millimeters), 0.85 inches wide (21.45 millimeters), and a bit more than 1/10th inch (2.8 millimeters) thick. For applications demanding even smaller media, Sony offers the Memory Stick Duo, which measures 1.25 inches (31 millimeters) by 0.75 inches (20 millimeters) and 1/16th inch (1.6 millimeters) thick.

The plastic package of each Memory Stick comes in one of two colors. The basic Memory Stick is blue. It is meant for general-purpose storage and holds nothing but memory and interfacing circuitry. A white Memory Stick has Sony's Magic Gate copy-management protocol.

Sony calls Memory Stick the de facto standard for digital networks. What that means is that Memory Stick does not bear the imprimatur of a recognized standards organization but lots of companies use the same design (under license from Sony). Currently five manufacturers offer Memory Stick products: Apacer Technology, Hagiwara Sys-Com Co. Ltd., I-O Data Device, Lexar Media, SanDisk, and Sony.

At one time, the Memory Stick format was more expensive than competing card formats. Now, Sony has licensed other manufacturers to make and sell Memory Sticks, and the price is competitive with other packages. Two Web sites are meant to provide information about Memory Sticks. The general public can access www.memorystick.com. Memory Stick licensees can access www.memorystick.org.

Multimedia Cards

Almost as a response to SmartMedia's claims to be the smallest, SanDisk Corporation and Siemens AG/Infineon Technologies AG developed the MultiMedia Card, which is less than half the size of the SmartMedia card (although twice as thick). According to its promoters, a MultiMedia Card is about the size of a postage stamp. That's true in a way (some commemorative postage stamps are nearly the size of envelopes). The MultiMedia Card (MMC) actually measures a little more than an inch square, at 24 by 37 mm and 1.4 mm thick (big for a stamp but small for a memory and exchange medium).

Designed specifically for memory, MultiMedia Cards were originally designed with a 64MB maximum capacity. Cards come in two types: ROM-based for prerecorded music (you cannot record on ROM), and Flash memory for recording your own music and photos.

The one-piece molded plastic package has seven gold pins on one edge to provide a serial interface.

To promote MultiMedia Card technology, 14 companies founded the MultiMedia Card Association in 1998. It has since grown to host over 100 members. The MultiMedia Card Association maintains a Web site at www.mmca.org.

Secure Digital

Derived from the MultiMedia Card, you can consider the Secure Digital card to be MMC with copy protection. The Secure Digital design is an obvious rethinking of the MultiMedia Card concept.

The Secure Digital card uses a nine-pin serial interface, similar to that of the MultiMedia Card. In fact, the two extra pins are grafted on to the layout of the older card design, with a small pin 8 crammed between pin 7 and the edge of the card. Pin 9 resides at the opposite side, adjacent to pin 1 but in the notch area.

The initial design of the Secure Digital card was thicker than the MultiMedia Card to allow the most complex circuitry required by its serial copy management electronics. The Secure Digital specifications also describe a "thin" card, one with the same 1.4 mm thickness of the MMC.

The Secure Digital card also incorporates a write-protect tab. By sliding the tab up the side of the card, you can prevent compliant electronic gear from disturbing the contents of the card. The specification also allows for a read-only card without a sliding tab.

The current designs of the Secure Digital card accommodates capacities from 32MB to 256MB.

Secure Digital Association

719 San Benito Street, Suite C

Hollister, CA 95023

Phone: 831-636-7322 (SDCA)

Fax: 831-636-2522

Email: sda@hollinet.com

xD Picture Card

The latest player in the memory card game is the xD Picture Card, announced July 30, 2002. Jointly developed by Olympus and Fuji Photo Film Company, this card is about the size of a postage stamp, as described by news releases from each company. In fact, the xD Picture Card is actually the smallest of the memory card formats. The standard card dimensions are 20 by 25 mm and 1.7 mm thick.

According to the developers, the name is taken from the phrase "Extreme Digital." Initially, Toshiba will manufacture the cards.

The card design allows for capacities up to 8GB per card, but initial real-world implementations store only 16 to 128MB.

Although only Fuji and Olympus cameras are initially slated to use the xD Picture Card, with an adapter it can also be used in place of PC Cards. A card reader with a USB interface was also introduced at the same time as the first cards, and a Compact Flash adapter is under development.

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