Portable devices using solid state can hold data for long periods, either as a backup for safekeeping or to transfer data between systems. Solid state RAM remembers the state it’s been set to when the power is removed, as opposed to the RAM used in PCs, which is wiped clean every time the PC is shutdown. There are two main forms in use, USB flash drives or memory cards.
USB Flash Drives
USB flash drives (variously referred to as memory sticks, memory drives, memory keys, pen drives or thumb drives) use the USB interface to connect to a PC. As well as being used to backup data and transfer it from one PC to another, they can be used to boot PCs, in a similar way to a floppy disk, CD or DVD (or indeed, a hard disk).
USB flash drives are not drives in the same sense as hard disk drives, as they have no moving parts and hence no “drive.” As there was no universally accepted name for these devices from the start, this has evolved into the most common term used today.
While USB memory sticks are most commonly used with PC’s, memory cards tend to be used in smaller non-PC devices such as mobile phones, cameras, PDAs and game consoles. Memory cards are used either to increase the capacity of the device or to provide a means of transferring pictures, movies or other data to a PC to be processed in some way.
Memory cards such as CompactFlash (CF) and Secure Digital (SD) cannot be used to transfer information directly to a PC. As they have proprietary interfaces there has to be an intermediate device such as a card reader. This can be a separate device that connects to the PC using USB or a card that goes into a PC Card (PCMCIA) slot in a laptop that cradles the memory card. Increasingly desktop PCs and Media PCs (PCs intended for use in a lounge connected to a TV) will come with a multi-format card reader installed.
The proprietary interfaces of memory cards give rise to their main disadvantage. There are so many different formats and interfaces, some interchangeable with others and some not, that it’s difficult for PC users to work out which format will fit in which device, or which format to use for a specific device or application.
USB flash drives, by contrast, are completely interchangeable as they use the USB standard, early ones using USB 1.0 or 1.1 and modern ones using USB 2.0. Even then, USB 1.x drives will work in USB2.0 slots and vice versa. Of course, their larger size makes them unsuitable for use in small devices.
The multitude of different memory card forms and interfaces that are now available have arisen partly because of practical and technical issues and partly because of commercial initiatives.
There are essentially four main formats:
- Sony’s proprietary Memory Stick
- CompactFlash (CF)
- Multi-Media Card (MMC) and its offspring SD
- XD card
Commercial issues gave rise to Sony’s format. By inventing their own format they can use it to tie customers into buying only Sony devices. So, for example, the only card reader you will find on a Sony laptop is a Memory Stick slot. Sony has expanded the range to around half-a-dozen versions in order to cater for the decreasing size of the devices they produce.
CF was one of the first memory cards to establish itself and remains the standard for medium to large sized cameras because of the large capacities it offers (over 32Gb) and relatively good cost-per-byte ratio. The CF interface has also allowed manufacturers to produce all sorts of CF-based devices such as wireless and bluetooth cards, CF hard disks and modems to name just a few. But its size prevented it from becoming the standard for the smaller devices such as mobile phones and newer, smaller PDAs and digital cameras.
The MMC and SD formats came later and were designed in a smaller size from the start with an eye to capturing that small device card market. MMC came first then SD arrived with the main distinguishing feature of a small write-protect switch similar to those on floppy disks (hence ‘Secure’ of SD). Now that phones and digital cameras in particular are becoming even smaller and, crucially, slimmer, both formats have had to come out with even smaller versions.
xD is the newest entrant into the market to gain acceptance. It was developed by Olympus and Fujifilm and intended to succeed CF. The cards are significantly smaller than CF but do not yet offer the same large capacities. Their crucial advantage is speed of data transfer, however, which is important for the large data size of high-resolution images captured by top-end professional digital cameras.
- Guide to SanDisk’s CompactFlash memory card
- MultiMediaCard (MMC) – SanDisk and Siemens NAND memory card for phones and smaller devices
- Secure Digital (SD) Cards – popular digital camera memory card format
- Guide to SmartMedia cards, introduced as Solid State Floppy Disk Cards (SSFDC)
- xD Picture Card , the Fuji and Olympus memory card
- USB Flash Drives
- Sony Memory Stick technology and background
- USB Flash Drives – USB stick, USB RAM, Memory Stick