One of the least understood aspects of buying CF (Compact Flash) or SD (Secure Digital) Memory Cards for your Digital Camera, Digital Video Camera, or MP3 Player, is the Speed Rating.

The card manufacturers do little to help the situation - their ads spouting a stream of numbers with no idea of what they really mean - leaving  most of us confused and bewildered, to put it mildly.  All that most of us grasp is that the higher the number, the faster the card is - which is true.  It is also true that the faster the card is, the more it costs - and many of us are paying, quite grandly, for card speeds well beyond what our devices can support, which is just a waste of money.

My aim here is to help you understand the Speed Ratings of these memory cards, and how they relate to the speeds actually needed by current devices.  This will help you to avoid buying more Speed than you need.  The money you save can be put into something more useful - like more gigabytes of memory capacity (which translates into being able to store more pictures or music for the same amount of money).

You will normally find memory card Speed Ratings listed as (whatever number)x - for example, 66x is a common one these days.  This expresses a data transfer rate based on an old rating standard, in which 1x = 150kb/second.  This could also be expressed as 0.15 Megabytes/second.

For use on a Digital Camera, not all camera manufacturers publish the Data Transfer Rate for their cameras, but a little web searching may well turn up a rating for yours.  As a guide, the latest DSLR's (such as my Sony Alpha 100 - which uses CF cards) will do around 9 MB/second - which would call for a 60x card speed.  A decent Point & Shoot model (such as my Canon PowerShot A540 - using SD cards) does 6-7 MB/second, requiring even less card speed.

So for current Digital Cameras, a 66x card - such as Sandisk's Ultra-II line - is quite sufficient for getting optimal operating speed from the camera.  A real hard-shooting Professional Photographer with a top-end future DSLR might, on rare occasion, hit the point where they would need a faster card (such as the 133x rated Sandisk Extreme-III series) to avoid any buffer delays in the heat of battle.  The rest of us will never notice the difference, because our cameras won't write faster than the card will take it.

Digital VIDEO Cameras, on the other hand, may have higher Data Transfer Rates - and are likely to progress to even higher transfer rates, well ahead of still cameras.  You will need to do some web research to learn the data rate of your particular video camera.  The higher the video resolution, the higher the data transfer rate likely is - and the more likely you will need a 133x (or higher) memory card to keep up with it.

MP3 music players are perhaps the least demanding for memory card speed.  The typical 128kb/second rate of an MP3 file, equates to less than 1x in the card speed rating system.  So your MP3 player will do just fine with the cheapest grade of memory card you can find - allowing you to concentrate your money on higher Gigabyte storage capacities.  And isn't that, after all, what you want in an MP3 player - MORE Music?