Flash Memory Devices

Flash memory has been around for several years as a main or an auxiliary storage medium for notebook computers. However, the rise of devices such as digital cameras and MP3 players and the presence of USB ports on practically all recent systems have transformed this technology from a niche product into a mainstream must-have storage technology.

Flash memory is a type of nonvolatile memory that is divided into blocks rather than bytes, as with normal RAM memory modules. Flash memory, which also is used in most recent computers for BIOS chips, is changed by a process known as Fowler-Nordheim tunneling. This process removes the charge from the floating gate associated with each memory cell. Flash memory then must be erased before it can be charged with new data.

The speed, low reprogramming current requirements, and compact size of recent flash memory devices have made flash memory a perfect counterpart for portable devices such as notebook computers and digital cameras, which often refer to flash memory devices as so-called "digital film." Unlike real film, digital film can be erased and reshot. Ultra-compact, USB-based keychain drives that use flash memory are replacing both traditional floppy drives and Zip/SuperDisk drives for transporting data between systems.

Types of Flash Memory Devices

Several types of flash memory devices are in common use today, including

ATA Flash
CompactFlash (CF)
SmartMedia (SM)
MultiMediaCards (MMC)
Reduced Size MMC (RS-MMC)
SecureDigital (SD)
MiniSD
Memory Stick
Memory Stick PRO
Memory Stick PRO Duo
xD-Picture Card
Thumb or keychain USB devices

Some of these are available in different sizes (Type I/Type II). Table 10.7 shows the various types of solid-state storage used in digital cameras and other devices, listed in order of introduction.

Table 10.7. Different Flash Memory Devices and Physical Sizes
Type	L (mm)	W (mm)	H (mm)	Volume (cc)	Date Introduced
ATA Flash Type II	54.00	85.60	5.00	23.11	Nov. 1992
ATA Flash Type I	54.00	85.60	3.30	15.25	Nov. 1992
CompactFlash (CF) Type I	42.80	36.40	3.30	5.14	Oct. 1995
SmartMedia (SM)	37.00	45.00	0.76	1.27	Apr. 1996
CompactFlash (CF) Type II	42.80	36.40	5.00	7.79	Mar. 1998
Memory Stick	21.45	50.00	2.80	3.00	Jul. 1998
Secure Digital (SD)	24.00	32.00	2.10	1.61	Aug. 1999
MultiMediaCard (MMC)	24.00	32.00	1.40	1.08	Nov. 1997
xD-Picture Card (xD)	20.00	25.00	1.70	0.85	Jul. 2002
Memory Stick Duo	20.00	31.00	1.6	0.99	Jul. 2002
Reduced Size MMC (RS-MMC)	24.00	18.00	1.40	0.60	Nov. 2002
MiniSD	20.00	21.5	1.4	0.59	Mar. 2003
MicroSD	15.00	11.00	1.0	0.165	Jul. 2005
Memory Stick Micro	15.00	12.5	1.2	0.225	Sep. 2005
Note: USB flash drives are not listed because they do not have a standardized form factor.

CompactFlash

CompactFlash was developed by SanDisk Corporation in 1994 and uses ATA architecture to emulate a disk drive; a CompactFlash device attached to a computer has a disk drive letter just like your other drives. Later types of flash memory also use ATA architecture, either implemented in the device itself or in its controller.

The original size was Type I (3.3mm thick); a newer Type II size (5mm thick) accommodates higher-capacity devices. Both CompactFlash cards are 1.433" wide by 1.685" long, and adapters allow them to be inserted into notebook computer PC Card slots. The CompactFlash Association (http://www.compactflash.org) oversees development of the standard.

SmartMedia

Ironically, SmartMedia (originally known as SSFDC for solid state floppy disk card) is the simplest of any flash memory device; SmartMedia cards contain only flash memory on a card without any control circuits. This simplicity means that compatibility with different generations of SmartMedia cards can require manufacturer upgrades of SmartMedia-using devices. The Solid State Floppy Disk Forum (http://www.ssfdc.or.jp/english) oversees development of the SmartMedia standard.

Tip

If you use a SmartMedia-based Olympus digital camera that has the panorama feature, be sure to use Olympus-brand SmartMedia because other brands lack support for the panorama feature.

MultiMediaCard

The MultiMediaCard (MMC) was codeveloped by SanDisk and Infineon Technologies AG (formerly Siemens AG) in November 1997 for use with smart phones, MP3 players, digital cameras, and camcorders. The MMC uses a simple 7-pin serial interface to devices and contains low-voltage flash memory. The MultiMediaCard Association (www.mmca.org) was founded in 1998 to promote the MMC standard and aid development of new products. In November 2002, MMCA announced the development of the Reduced Size MultiMediaCard (RS-MMC), which reduces the size of the standard MMC by about 40% and can be adapted for use with standard MMC devices. The first flash memory cards in this form factor were introduced in early 2004 to support compact smart phones.

SecureDigital

A SecureDigital (SD) storage device is about the same size as MMC (many devices can use both types of flash memory), but it's a more sophisticated product. SD, which was codeveloped by Toshiba, Matsushita Electric (Panasonic), and SanDisk in 1999, gets its name from two special features. The first is encrypted storage of data for additional security, meeting current and future Secure Digital Music Initiative (SDMI) standards for portable devices. The second is a mechanical write-protection switch. The SD slot can also be used for adding memory to Palm PDAs. The SDIO standard was created in January 2002 to enable SD slots to be used for small digital cameras and other types of expansion with various brands of PDAs and other devices. The SD Card Association (http://www.sdcard.org) was established in 2000 to promote the SD standard and aid the development of new products. Note that some new laptop computers have built-in SD slots.

Reduced-size versions of SD include MiniSD (introduced in 2003) and MicroSD (introduced in 2005). MiniSD and MicroSD are very popular choices for smart phones, and can be adapted to a standard SD slot. MicroSD is compatible with the TransFlash standard for mobile phones.

Sony Memory Stick and Memory Stick Pro

Sony, which is heavily involved in both notebook computers and a wide variety of digital cameras and camcorder products, has its own proprietary version of flash memory known as the Sony Memory Stick. This device features an erase-protection switch, which prevents accidental erasure of your photographs. Sony has also licensed Memory Stick technology to other companies, such as Lexar Media.

Lexar introduced the enhanced Memory Stick PRO in 2003, with capacities ranging from 256MB up to 1GB. Memory Stick Pro includes MagicGate encryption technology, which enables digital rights management, and Lexar's proprietary high-speed memory controller. Memory Stick Pro is sometimes referred to as MagicGate Memory Stick.

The Memory Stick Pro Duo is a reduced-size, reduced-weight version of the standard Memory Stick Pro. It can be adapted to devices designed for the Memory Stick Pro.

ATA Flash PC Card

Although the PC Card (PCMCIA) form factor is now used for everything from game adapters to modems, from SCSI interfacing to network cards, its original use was computer memory, as the old PCMCIA (Personal Computer Memory Card International Association) acronym indicated.

Unlike normal RAM modules, PC Card memory acts like a disk drive, using the PCMCIA ATA (AT Attachment) standard. PC Cards come in three thicknesses (Type I is 3.3mm, Type II is 5mm, and Type III is 10.5mm), but all are 3.3" long by 2.13" wide. Type I and Type II cards are used for ATA-compliant flash memory and the newest ATA-compliant hard disks. Type III cards are used for older ATA-compliant hard disks; a Type III slot also can be used as two Type II slots.

xD-Picture Card

In July 2002, Olympus and Fujifilm, the major supporters of the SmartMedia flash memory standard for digital cameras, announced the xD-Picture Card as a much smaller, more durable replacement for SmartMedia. In addition to being about one-third the size of SmartMediamaking it the smallest flash memory format yetxD-Picture Card media has a faster controller to enable faster image capture. Currently, xD-Picture Cards are available in capacities of 16MB1GB.

16MB and 32MB cards (commonly packaged with cameras) record data at speeds of 1.3MBps, whereas 64MB and larger cards record data at 3MBps. The read speed for all sizes is 5MBps. The media is manufactured for Olympus and Fujifilm by Toshiba, and because xD-Picture media is optimized for the differences in the cameras (Olympus's media supports the panorama mode found in some Olympus xD-Picture cameras, for example), you should buy media that's the same brand as your digital camera.

USB Keychain Drives

As an alternative to floppy and Zip/SuperDisk-class removable-media drives, USB-based flash memory devices are rapidly becoming the preferred way to move data between systems. The first successful drive of this typeTrek's ThumbDrivewas introduced in 2000 and has spawned many imitators, including many that incorporate a keychain or pocket clip to emphasize their portability.

Note

Some USB flash memory drives are even built in to pens or knives, such as the Victorinox SwissMemory Swiss Army Knife, with capacities up to 1GB.

Unlike other types of flash memory, USB keychain drives don't require a separate card reader; they can be plugged in to any USB port or hub. Although a driver is usually required for Windows 98 and Windows 98SE, most USB keychain drives can be read immediately by newer versions of Windows, particularly Windows XP. As with other types of flash memory, USB keychain drives are assigned a drive letter when connected to the computer. Most have capacities ranging from 128MB to 1GB, with some capacities as high as 2GB or more. However, typical read/write performance of USB 1.1-compatible drives is about 1MBps. Hi-Speed USB keychain drives are much faster, providing read speeds ranging from 5MBps to 15MBps and write speeds ranging from 5MBps to 13MBps. Because Hi-Speed USB keychain drives vary in performance, be sure to check the specific read/write speeds for the drives you are considering before you purchase one.

Tip

If you have a card reader or scanner plugged in to a USB hub or port on your computer, you might need to disconnect it before you can attach a USB keychain drive. This is sometimes necessary because of conflicts between the drivers used by some devices. Use the Windows Safely Remove Hardware icon in the system tray to stop the card reader before you insert the USB keychain drive. After the USB keychain drive has been recognized by the system, you should be able to reattach the card reader.

For additional protection of your data, some USB keychain drives have a mechanical write-protect switch. Others include or support password-protected data encryption as an option, and some are capable of being a bootable device (if supported in the BIOS). The Kanguru MicroDrive+ can be upgraded with SD or MMC flash cards for additional capacity. Some drives feature biometric securityyour fingerprint is the key to using the contents of the drivewhereas others include more traditional security software.

If you use MMC, SD, xD-Picture Card, Memory Stick, or Memory Stick Pro flash memory cards in digital cameras or other devices, you can use them as interchangeable storage in the Lexar Media Single-Slot Multi-Card Reader. This device is essentially a USB (1.1/2.0) keychain drive without flash memory storage onboard. You can use it as a card reader or as a USB drive with removable storage.

Note

Older models of the Lexar Single-Slot Multi-Card Reader were sold as the Jump Drive Trio and supported MMC, SD, or Memory Stick media only.

SimpleTech's Bonzai USB 2.0 flash drive provides similar functionality for SD and MMC cards only and is available with or without preinstalled SD or MMC memory.

Comparing Flash Memory Devices

As with any storage issue, you must compare each product's features to your needs. You should check the following issues before purchasing flash memory-based devices:

Which flash memory products does your camera or other device support? Although adapters allow some interchange of the various types of flash memory devices, for best results, you should stick with the flash memory type your device was designed to use.
Which capacities does your device support? Flash memory devices are available in ever-increasing capacities, but not every device can handle the higher-capacity devices. Check the device and flash memory card's websites for compatibility information.
Are some flash memory devices better than others? Some manufacturers have added improvements to the basic requirements for the flash memory device, such as faster write speeds and embedded security. Note that these features usually are designed for use with particular digital cameras only. Don't spend the additional money on enhanced features if your camera or other device can't use those features.

Only the ATA Flash cards can be attached directly to a notebook computer's PC Card slots. All other devices need their own socket or some type of adapter to transfer data. Figure 10.10 shows how the most common types of flash memory cards compare in size to each other and to a penny.

Figure 10.10. SmartMedia, CompactFlash, MultiMediaCard, SecureDigital, xD-Picture Card, and Sony Memory Stick flash memory devices. Shown in relative scale to a U.S. penny (lower right).

Table 10.8 provides an overview of the major types of flash memory devices and their current capacities. Note that smaller-capacity cards might be bundled with some digital cameras.

Table 10.8. Flash Memory Card Capacities
Device	Minimum Capacity	Maximum Capacity	Notes
CompactFlash+	16MB	8GB	Highest capacity; most flexible format; supported by most digital SLR cameras. Lexar Media and SanDisk also make faster versions of CF+ media; Lexar Media also makes LockTight secured access media.
SmartMedia	16MB	128MB	Popular choice for older Fujifilm and Olympus digital cameras.
MultiMediaCard (MMC)	16MB	128MB	MMC cards can work in most SD slots.
RS-MMC	128MB	1GB	Use adapter to plug in to MMC slots.
Secure Digital (SD)	16MB	1GB	SD cards do not work in MMC slots. Used by most brands of consumer-level digital cameras.
MiniSD	128MB	1GB	Use adapter to plug in to SD slots.
MicroSD	128MB	128MB	Use adapter to plug in to SD slots.
Memory Stick	16MB	128MB	This was developed by Sony and licensed to other vendors.
Memory Stick PRO (also known as Memory Stick Magic Gate)	256MB	1GB	This is the enhanced high-speed version of Memory Stick (also known as with digital nights management support.
Memory Stick Pro Duo	256MB	512MB	Reduced-size version of Memory Stick PRO.
ATA Flash	16MB	2GB	This plugs directly into a PC Card (PCMCIA) slot without an adapter.
xD-Picture Card	16MB	1GB	Use the same brand as your digital camera for the best results.
USB keychain drive	16MB	2GB	Some include password-protection and write-protect features.

I normally recommend devices (cameras, PDAs, and so on) that use CompactFlash (CF), Secure Digital (SD), or xD-Picture flash memory cards. Any of the others I generally do not recommend due to limitations in capacity, performance, proprietary designs, and higher costs.

CompactFlash is the most widely used format in professional and consumer devices and offers the highest capacity, at the lowest prices, in a reasonably small size. CF cards plug directly into PC Card slots on all laptops by using a simple passive adapter that is extremely inexpensive. Therefore, when you're not using one of those cards in your camera, you can use it as a solid-state hard disk in a laptop. For a long time I would not even consider a camera or other device that did not use CF storage. I have relaxed on that stance a little bit, but it is still by far the best overall format and is available in capacities of up to 8GB or higher. It is also significantly faster than the other formats.

Secure Digital has become quite popular, is reasonably fast, and is available in capacities up to 1GB. SD sockets also take MultiMediaCard (MMC) cards, which are basically thinner versions of SD. Note that the opposite is not trueMMC sockets do not accept SD cards. MMC is also available in versions up to 128MB; the MMC Mobile developed by SanDisk reaches capacities of 256MB. Finally, xD-Picture is a very compact format that has grown in popularity and offers capacities up to 1GB.

In general I would not consider any device that uses other formats, especially Memory Stick, which is a Sony proprietary format (didn't Sony learn anything from the Betamax versus VHS war?). The RS-MMC format is too new to consider and as such is found in a limited number of devices with very limited capacity. ATA Flash is great, but the cards are physically big, mostly obsolete, and can easily be replaced by a CompactFlash card in a PC Card adapter. SmartMedia was once a popular format, but it's relatively fragile now and is limited to 128MB in capacity, and camera vendors who once used it have now switched to the higher-capacity xD-Picture card format.

Moving Data in Flash Memory Devices to Your Computer

Several types of devices can be purchased to enable the data on flash memory cards to be moved from digital cameras and other devices to a computer. Although some older digital cameras come with an RS-232 serial cable for data downloading, this is a painfully slow method, even for low-end cameras with less than a megapixel (1,000 pixel horizontal width) resolution.

Card Readers

The major companies who produce flash card products sell card readers that can be used to transfer data from proprietary flash memory cards to PCs. These card readers typically plug in to the computer's USB ports (some older versions might use the parallel port) for fast access to the data on the card.

In addition to providing fast data transfer, card readers enable the reuse of expensive digital film after the photos are copied from the camera and save camera battery power because the camera is not needed to transfer information. External card readers can be used with any computer with the correct port type and a supported operating system. USB readers, for example, should be used with Windows 98 or above. Some older readers don't support write functions (such as erasing pictures after they're transferred from the media to your computer); I recommend devices with read/write functionality.

Because many computer and electronics device users might have devices that use two or more types of flash memory, many vendors now offer multiformat flash memory card readers, such as the SanDisk 12-in-1 Card Reader/Writer shown in Figure 10.11.

Figure 10.11. The SanDisk 12-in-1 Card Reader/Writer plugs into a Hi-Speed USB (USB 2.0) port and features a removable stand. Photo courtesy of SanDisk.

Before you purchase a card reader, check your PC and your photo printer. You might already have a card reader built in to your PC or photo printer. Many PCs, including those that use Windows XP Media Center Edition, include a three- or four-slot card reader built in to the front panel. This type of card reader plugs into a USB port header on the motherboard.

Figure 10.12 shows the integrated card reader built in to an Epson Stylus Photo R300 printer. A Compact Flash card is inserted into the printer.

Figure 10.12. A three-slot card reader built in to an Epson Stylus Photo R300 inkjet printer.

Type II PC Card Adapters

For use in the field, you might prefer to adapt flash memory cards to the Type II PC Card or CardBus slot found in most notebook computers. You insert the flash memory into the adapter; then, you slide the adapter into the notebook computer's Type II PC Card slot. Figure 10.13 shows how a CompactFlash card Type II PC Card adapter works. As with card readers, check with the major companies that produce your type of flash memory device for the models available.

Figure 10.13. A typical Type II PC Card adapter for CompactFlash media (left) compared to an ATA DataFlash card (right).

Key Factors in Selecting a Removable-Media Drive

When shopping for a removable-media drive, keep the following in mind:

Price per megabyte/gigabyte of storage. Take the cost of the drive's cartridge or disk and divide it by the storage capacity to see how much you are paying per megabyte or gigabyte of storage. This difference in price becomes quite apparent as you buy more cartridges or disks for the drive. (Don't forget to factor in the cost of the drive itself if you are trying to decide which removable-media drive to buy!) If you plan to use removable storage for temporary data storage only, as with flash memory devices, the cost per megabyte or gigabyte is a less important factor than if you plan to leave data on a cartridge or disk for long periods of time.
Access time versus need of access. The access and data transfer speeds are important only if you need to access the data frequently or quickly. If your primary use is archiving data, a slower drive might be fine. However, if you plan to run programs off the drive, choose a faster drive instead.
Compatibility and portability. For maximum portability and compatibility, opt for a USB-based solution. Although some removable-media drives also support FireWire (IEEE 1394), SCSI or parallel ports, Hi-Speed USB is the lowest-cost and friendliest solution because it's built in to recent systems, supports hot-swapping, and can be used on machines with USB 1.1 ports (albeit with much slower data transfer and access speeds). Also verify that drivers are available for each type of machine and operating system you want to use with the drive, and consider whether you need to exchange disks with other users. If you don't want the expense of buying a separate drive for each machine, USB keychain storage devices using flash memory or USB-based external hard disks can perform the same tasks and don't need a separate drive for each computer. For some users, this might be the most important factor in choosing a drive.
Storage capacity. For maximum safety and ease of use, the capacity of your storage device should be the largest available that meets your other requirements. Digital camera users, for example, will want the largest possible flash or disk storage supported by their cameras to allow more photos or higher-quality photos to be stored. Desktop and notebook computer users will want the largest drives possible for data backup or program storage.
Note

For many uses, the rewritable DVD drive is the best choice for two reasons: low media cost (well under $1 each in quantity for CD-RW media; less than $3 each for rewritable DVD) and near-universal compatibility (virtually all systems sold since the mid-1990s can read CD-RW media in ordinary CD-ROM drives, and many systems with DVD-ROM drives can read rewritable DVD media). For permanent storage, use CD-R or recordable DVD media.

USB keychain drives are now available in capacities above 1GB for situations demanding high storage density in a very small space.
Internal versus external. Most users find external USB drives the easiest to install; additionally, they give you the option of using the drive on several systems. Internal drives are usually faster because of their ATA, Serial ATA, or SCSI interfaces and are more cleanly integrated into the system from a physical perspective.
Bootable or not. Most systems dating from 1995 or later have a BIOS that supports the Phoenix El Torito standard, which enables them to boot from CD or DVD drives or drives that emulate them, such as the Iomega REV. Most also support the ATAPI/IDE version of the Imation LS-120 or LS-240 SuperDisk as a bootable device; however, those drives are obsolete and difficult to find. Some systems support ATA Zip drives as a bootable drive, but Zip drives are a proprietary format and incompatible with standard 3 1/2" floppy disks. The newest systems support USB floppy drives for booting, enabling you to dispense with a traditional internal floppy disk drive for diagnostics or mass storage device driver installation.

Use the Disk Management snap-in module in Windows 2000 and Windows XP to change the drive letter assigned by Windows to a removable-media drive. With older versions of Windows, the next available drive letter will be assigned and cannot be changed.