Articles: Storage

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Many of us are busy increasing the amounts of graphical information about the world around us by using a digital camera or a camcorder. Besides choosing the image capturing device proper, we have to face the problem of choice of the memory card. Owners of cheap cameras just have to choose the type and capacity they need. The speed characteristics of the card aren’t important for them since most available memory cards will suit such cameras. But people who have more serious devices, perhaps professional-level mirror-based cameras, have to approach the problem of choice more carefully. The speed of reading from the card may also be important, for example for journalists. When you’ve got some hot material on your card, you have to send the photos to your agency as quickly as possible. High speed is also needed by owners of camcorders with flash memory and by users of mobile devices like PDAs, players, media-centers and notebooks. Why do you need a memory card in your notebook? Because it is a small and universal data storage device that consumes very little power.

Last year SanDisk announced a new series of high-speed Compact Flash memory cards for this broad user audience and accompanied it with a release of two new card-readers with FireWire and USB interfaces. With capacities up to 8GB, this card series delivers read and write speeds up to 40MB/s, according to the manufacturer. For comparison, the previous high-speed Compact Flash series from the same brand, Extreme III, delivered only half that speed, 20MB/s. Compared with the CD speeds, 40MB/s equals 266x.

Is this speed really high for practical applications? Let’s evaluate it by using images in RAW format which stores raw, unprocessed data from the camera’s array and provides broad opportunities for further processing. This format results in very large files. One frame from a 10-megapixel array (such arrays are currently employed in top-end amateur cameras and in popular mirror-based cameras like Canon 400D, Nikon D80, Pentax K10D and Sony Alpha) is as large as 10-15MB in RAW format, depending on how complex the image is. Easy to calculate, the flash card is fast enough to capture at a rate of 3-4 such frames per second. For a majority of cameras, except for professional-level mirror cameras, this speed is the maximum the camera controller and the shutter can do, and the memory card won’t be a bottleneck. The speed of the card-reader integrated into the camera may also be a bottleneck, of course, but that is the camera maker’s rather than the card maker’s problem.

If you have been reading our reviews of portable storage media, you already know that the data-transfer rate of 40MB/s is unachievable with the USB interface. This is why two card-readers were introduced for the new series of SanDisk flash cards. The one with a USB interface is for ordinary speeds while the FireWire-interfaced version is for those who need the maximum possible data-transfer rate.

If you want to know a bit of history, read the following section about the story of Compact Flash format and its technicalities. And then we will tell you more about the devices we are going to test today.

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