Flash memory chips have appeared in more than 20 memory card formats. Only a few remain – USB stick, Compact Flash, Secure Digital and Sony’s Memory Stick are the survivors, along with the proprietary formats of major game console vendors, and mobile phone SIM cards.
Smart Media
Now almost defunct, Smart Media was the first card memory released with NAND Flash. It often had only a single flash chip mounted in a very thin, flat card and no built-in controller. This led to address compatibility problems as capacities increased and Smart Media ceased production with 128MB cards. With its limited connections it’s also slower than the competing Compact Flash card. There are many digital cameras still in use that use Smart Media memory.
USB memory sticks
USB Flash memory, also sometimes referred to as thumbdrive, Jumpdrive (a Lexar marketing name) or a USB key, is by now familiar to most people and has largely usurped the floppy disk. It’s ideal for temporary backups and file transfer, but USB keys stick out when plugged in so don’t suit semi-permanent installation, unlike most of the other Flash formats. The connector is simple, but transfer rates are limited by the USB port, so a USB2 memory key will run slowly in a USB1 port. Unlike Smart Media, they include a controller chip to perform maintenance duties and filing system conversion. One of the larger forms of Flash, USB sticks are sometimes fitted with write-protect switches and almost always have an activity light. They’re typically available in capacities from 256MB to 32GB and with transfer rates up to 22Mbytes/sec. Besides capacity and speed, the price of USB Flash is determined by features such as metal cases, extras such as encryption or displays showing usage.
Compact Flash (CF)
Compact Flash, based on the PC Card and introduced by Sandisk in 1994, is one of the oldest Flash card hardware configurations and, although the casing is relatively bulky, the CF card has proven to have great staying power. Along with Smart Media, Compact Flash was a success in digital cameras, where it is still commonly used. CF is made in two types; Type I is 3.3mm thick and Type II 5mm thick. Type II is used for micro hard drives and is now quite rare. CF also comes in four speeds; the original CF, CF High Speed (also known as CF+ or CF 2.0 or II) with a typical 10Mbytes/sec read and 9Mbytes/sec write, CF 3.0 (or III) with a typical 20Mbytes/sec read and write and CF 4.0 (or IV) with a typical 40Mbytes/sec read and write. Although the package size and connector for Compact Flash add to the manufacturing cost, the connector means CF has a wide, parallel, data bus and this is partly why the popular format has remained. It allows some CF cards to support Ultra Direct Memory Access (UDMA) for a 300X (45Mbytes/sec) transfer rate, providing the device they are plugged into supports UltraDMA, which some high-end digital cameras now do. In theory, revision 4.0 of the standard supports up to 133Mbytes/sec, and seek times for DMA-capable CF cards can beat those of a hard drive. Capacities range from 32MB up to 64GB and the cards themselves include a controller chip to perform wear mapping and filing system conversion.
Secure Digital (SD)
Secure Digital or SD cards and the associated formats miniSD, microSD, SDHC (SD High Capacity) miniSDHC and microSDHC, are perhaps today’s rising stars of Flash. SD memory is physically small and light, so it’s eminently suitable for use in handheld digital devices such as pocket cameras. The name Secure Digital is used because the original formats – SD and SDHC – are fitted with a tiny mechanical writeprotect slide switch. High Capacity, as in SDHC, refers to cards with capacities over the 2GB partition size limit imposed by Fat; these ‘HC’ devices use the Fat32 format instead. The mini and micro cards don’t have a switch, but can be inserted into an adapter that does, and allows them to fit SD slots. Transfer rates for SD are 10Mbytes/sec for the low-capacity, minimum-specification cards, up to 20Mbytes/sec for the highest specification cards.
Sony Memory Stick
Memory Stick is a proprietary Sony product, designed to lock users of their devices into using only this format. There are five flavours of Memory Stick; the original, the Memory Stick Micro, the MS Duo, the MS Pro Duo, and the MS Pro-HG Duo, with a maximum capacity of 32GB. According to Sony the newer MSmicro is designed for use in mobile phones and the company no longer supports the original Memory Stick. The MS Micro is available in 512MB, 1, 2 and 4GB capacities and the MS Duo is available only in 128MB. The MS Pro-Duo is available in 512MB, 1, 2, 4 and 8GB capacities. All three have a maximum transfer rate of 20Mbytes/sec. The MS Pro-HG Duo is available in 1, 2 and 4GB capacities with a maximum transfer rate of 30Mbytes/sec. Memory Stick is one of the few removable Flash memory formats that supports DRM (Digital Rights Management), in the form of Sony’s Magicgate.
