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Flash Memory Cards Buying GuideBuyers' Guide to Flash Memory Cards Contents
------------------------------------------------------------------------------------- There are dozens of memory card formats and making the right choice when buying one can make the difference between spending a fortune on a chunk of plastic or buying the right tool for the job. This guide will introduce you to the different memory card formats on the market and give you a buyer's overview of what to look out for when purchasing memory cards. Flash Memory lies at the heart of every memory card -- and every USB Key, iPod Nano and a number of other storage-based devices. Unlike the memory in your PC, which is erased every time the power is switched off, Flash Memory is non-volatile, meaning it retains information without an external power source. Originally devised by Japanese researchers working for Toshiba, Flash Memory has become the storage medium of choice for memory cards because it's relatively cheap to produce, quite shock resistant and able to be written to and from millions of times before the card expires. NOR and NAND are logic gates that define how an action will be performed. Without going into the basics of logic programming, the only thing you need to know about NOR and NAND from a consumer viewpoint is that pretty much all new Flash Memory is built as NAND Flash Memory. The earliest flash memory was NOR based, but NAND has overtaken it, largely due to the reliability of the media. NOR memory typically won't last beyond 100,000 write/erase cycles (and sometimes much less), while NAND Memory can manage up to a million such cycles. Memory cards: Form defines function The most common use of memory cards in the consumer world today is as storage media for digital cameras, often referred to as digital film. There are a number of different formats and vendors will talk up the advantages of their format (because they want your money), but for the most part, your choice of card isn't all that open to you. What you can use is largely determined by the devices you already have, or those you plan to buy. While there's some cross compatibility between certain formats -- SD-compatible readers can normally handle MMC, for example -- for the most part if your camera takes, Memory Stick, for example, then that's what you'll end up using.
CompactFlash is one of the oldest memory card formats still in current use, and its survival can be directly linked to the fact that it has been embraced by the professionals, especially for use in professional level digital cameras. CompactFlash cards are easily identified as they are physically larger than the other formats. There are two standards in the CompactFlash world, appropriately titled CompactFlash Type I and CompactFlash Type II. Both use casings that are 43mm wide and 36mm deep, but CompactFlash Type II cards are considerably thicker than their Type I counterparts -- 5mm to 3.3mm respectively. The size difference also means that Type I slots can't accommodate Type II cards, although Type II slots can take Type I cards. Typically speaking, Type I cards use flash-based memory, while the majority of Type II CompactFlash devices incorporate Microdrive-like miniature hard drives (see "Microdrives" below).
The size of CompactFlash may seem like a drawback for portable devices, but as a design CompactFlash has certain marked advantages. For a start, the CompactFlash standard is electrically identical to the PCMCIA standard, meaning that with the use of an adapter CompactFlash cards can be directly plugged into notebook PCs. The larger size of CompactFlash slots in devices has allowed wily device manufacturers to make adapters for other common storage media that fit within the slot -- so it's feasible to use an SD card in a CompactFlash slot, something that's physically impossible in reverse. CompactFlash write speeds vary depending on the standard used; the CompactFlash Specification 2.0 supports data rates of up to 16MBs, while the 3.0 specification supports rates of up to 66MBs. Electrically, CompactFlash supports voltages of 3.3V and 5V, and any compliant card should support both voltages. CompactFlash cards are also available in packaging that supports operation in extreme temperature variants, from -40 C to +85 C. The larger package size, market position in the professional space and electrical PCMCIA compatibility means that CompactFlash is also used for a variety of other applications such as miniature network cards. Microdrives are CompactFlash Type II sized miniature portable hard drives, initially developed by IBM in 1999. Development is now handled by Hitachi after the company purchased IBM's hard disk division in 2002. Unlike flash-memory based devices, Microdrives use actual miniaturised hard drives with read heads and moving parts. This makes them more susceptible to drop shock and associated problems, although they are remarkably resilient devices in actual use.
Memory Stick is Sony's proprietary standard for portable memory storage. As a standard, it's been around since 1998, and since then the company has developed several different Memory Stick products. The initial Memory Stick format is for a small stick measuring 50mm x 21.5mm x 2.8 mm with capacities up to 128MB. This rather meagre storage offering was quickly outpaced and even with the introduction of a switchable Memory Stick variant (Memory Stick Select) -- which had two identically sized banks of memory that the user could switch between -- larger capacities were needed to keep pace with Sony's array of Memory Stick compatible devices. That's when the Memory Stick Pro format was launched; it supports storage sizes currently up to 4GB with write speeds at a minimum of 15Mbs. This is not where standards stop, however. There is also a series of miniature memory stick variants, the Memory Stick Duo, the Memory Stick PRO Duo, and the Memory Stick PRO (High-Speed) Duo are used in mobile phones (mostly Sony Ericsson ones) and devices like Sony's PlayStation Portable. A Memory Stick PRO (High-Speed) Duo is the same as Memory Stick PRO Duo, except the read/write speed is increased to 80Mbps (when used with a compatible product). They measure in at a tiny 31mm x 20mm x 1.6mm. Adapters are available to physically upsize Memory Stick Duo products so that they can be used in devices that support full-sized Memory Stick products.
Sony has also recently announced an even smaller Memory Stick standard -- Memory Stick Micro. There aren't any Memory Stick Micro products available at the time of writing but the first products are expected in early 2006. Memory Stick Micro is pitched firmly at the mobile phone market, as it's very small (15mm x 12.5mm x 1.2mm) and has very low power consumption, using either 3.3V or 1.8V of power. To extend the range, Sony mixes and matches technologies; Memory Stick Duo also has a Memory Stick Pro Duo variant, for example, with higher data transfer rates and storage speeds. All of the Memory Stick standards support MagicGate, a Sony technology that enforces copyright on encrypted copyright material such that content can be copied to the Memory Stick for playback, but not copied off it to a different device. The feature-rich Pro sticks -- be they Memory Stick Pro or Memory Stick Pro Duo -- cost more than the plainer variants. Practically speaking, you're not likely to run across much non-Pro original Memory Stick media outside of eBay, but it's worth making sure that the Memory Stick that you're buying is compatible with your device. Sony has put memory stick slots in everything from mice to laptops, mobile phones to digital cameras and even USB Keys, but older devices may not be able to handle newer formats. Generally speaking, backwards compatibility isn't a problem in the Memory Stick world, although you can't use a physically larger Memory Stick in a Memory Stick Duo or Micro slot. What is SD/MMC/RS-MMC/MMC Micro/miniSD/MicroSD? Secure Digital (SD) media is a very common format that has grown out of the MultiMedia Card (MMC) standard. MMC dates back to 1997 and describes a 24mm x 32mm x 1.5mm storage card of varying capacities. MMC cards have largely been superseded by SD equivalents, although many Nokia mobile phone devices still use MMC cards. SD cards measure 32mm x 24mm x 2.1mm, making them slightly thicker than MMC cards, but as the two devices are identically configured, any SD-compatible device can read and write to MMC cards. Owing to the increased thickness of SD cards, the reverse isn't true. SD and MMC cards are supported by a wide variety of digital camera makers, as well as manufacturers of portable media players and PDAs, including Kodak, Canon and Samsung. The secure part of Secure Digital comes from the included but virtually never activated encryption hardware within an SD card. It's the equivalent of Sony's MagicGate technology, and about as welcome to the average consumer.
Just as Sony has several variants of the Memory Stick, there are smaller mobile-phone centric variants of both the MMC and SD standard. On the MMC side, there is the Reduced-Size Multimedia Card (RS-MMC), which at 24mm x 16mm x 1.5mm is essentially a half-size MMC card. The interesting factor with RS-MMC is that it's the same width as a regular SD or MMC card, and can thus be read (with an adapter) in any SD or MMC slot. RS-MMC is manufactured by SanDisk, while Samsung has another reduced size MMC variant, known as MMC-micro. MMC Micro cards measure in at 12mm x 14mm x 1.1mm, making them smaller than RS-MMC, but without the cross-compatibility of that format. Not to be outdone in confusing consumers, there are also two small SD card formats to ponder. The MiniSD card format calls for a card 20mm x 21.5mm x 1.4mm, and was introduced as a mobile media standard in 2003. One of these standards is seemingly never enough, and the SD Association announced an even smaller standard, MicroSD, in 2005. MicroSD holds the distinction of being the smallest portable media format, narrowly edging out Sony's Memory Stick Micro. MicroSD cards are tiny -- just 11mm x 15mm x 1mm, and while it's a format that has been accepted by the SD Association, it was originally solely developed by SanDisk under the TransFlash moniker. Smart Media is the oldest of the portable media formats still in (limited) use today, dating back to 1995. Originally envisaged as part portable media device, part replacement floppy -- hence its initial weighty nomenclature of Solid State Floppy Disk Card (SSFDC), it is notable for the now restrictive size limitations on individual cards -- which top out at 128MB -- and the fact that at 0.76mm thick, it's the thinnest of the portable memory card formats. Very few new devices support Smart Media cards natively due to the size restrictions of the format, although it's not unusual to see multi-card readers that support it for backwards compatibility purposes.
XD-Picture card is a standard jointly developed by Olympus and Fujifilm, so it should come as little surprise that Olympus and Fujifilm digital cameras are the primary places you'll find the tiny (20mm x 25mm x 1.78mm) card in use. XD (stands for eXtreme Digital) cards come in sizes from 16MB up to 1GB, with read/write speeds that vary from 5MBs/1.3MBs up to 3MBs/5MBs. However, the highest capacity cards (over 512MB) use a different internal architecture that gives them extra capacity but this comes at the expense of lower read/write speeds and some compatibility issues with certain older cameras. Storage availability within memory cards has risen over the years, but there's also a class of products that do more than offer memory card storage. One of the most popular additional features to add to a flash memory card is wireless network connectivity, generally utilising the slower 802.11b WiFi standard. Memory cards are available from a variety of manufacturers across different memory card formats that support WiFi access, although you'll need a device (usually a PDA or Smartphone) that will actively support WiFi connections. It's not purely limited to the PDA world, however, Sony used to offer a WiFi Memory Stick for its now locally discontinued Aibo Robot Dog. The one thing to bear in mind with any feature-enhanced memory card is that all the extra functionality comes at a price, usually in the amount of power that the device needs to draw. USB Keys -- sometimes referred to as Thumb drives, Pen Drives or Flash Drives or other such appellations -- are in essence NAND Flash Memory chips attached to some simple logic circuitry for read/write operations and a USB plug.
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Where Microdrives score highly is in the capacity they're able to offer -- Hitachi recently announced 8GB Microdrives -- at a much more compelling price point than solid-state alternatives. Because they have moving parts to operate, Microdrives do draw more power than other solid-state CompactFlash devices, and some Compact Flash-compatible devices may not be able to utilise Microdrives, or may suffer much lower battery life when they do. Again it's the professional world that has embraced Microdrives, especially in the professional camera world, where multi-gigabyte Microdrives were the norm while competing formats were topping out at the 512MB limit. 
Sizes for USB Keys run from 8MB up to 8GB with accordingly larger price tags as you require more storage. They're primarily designed as storage media for PC applications, although there are devices that will enable you to use USB Keys with other devices such as home game consoles. Older USB Keys work from the slower USB 1.1 specification, while current devices use the quicker USB 2.0 specification.