Contact
SubscribeMemory Card Speed Guide
The speed at which your memory card reads and writes doesn’t seem especially important when buying and this is both rightly so and cause for concern. If you use the standard 100-133x (times) cards you will probably not even realise they are kinda slow, but if your camera is less than a few years old the odds are you can go a lot faster.
Allow me to explain why memory card speed is important to you as a user. Most camera’s have a small amount of built in ‘RAM’ which is like a little memory card which they call a Buffer. The Buffer is where the picture goes when you take it, before it goes to the memory card. On larger images this accounts for that delay between taking a photo and being able to view the photo. Most Buffers can hold a few images even on the most basic of camera’s so its generally not an issue.
Now simply put your photo-sensor outputs the image data to the buffer, the buffer outputs this to the memory card which saves it. This means the faster your memory card the quicker the buffer empties, and the quicker and more photo’s you can take before the camera pauses to catch up.
How many times has your camera paused while taking photo’s and you’ve missed something you know would have been an amazing shot, but now its gone ? A faster card would have cut this pause in half, so a 10 seconds on a 66x, would have been 5 seconds on a 133x, 2.5 seconds on a 266x, 1.3 seconds on a 400x, and would barely even notice it on a 600x card. You can see easily how speed is something easy to miss but totally makes sense that the extra few quid is worth it when things are critical or once only events.
The Speed Calculation
Most memory cards measure their emulation speed in “x” ratings, where “x” is short for times or multiples, e.g. 8x, 20x, 133x. This is the very same speed measurement system used for CD-ROMs and indicates the maximum transfer rate in the form of multiplier of the data rate of an audio CD, which is 150 KB/s.
Emulation Speed = R * K
Where R = transfer rate (150KB/s), K = speed rating (133x). So using 133x as a speed rating means transfer speed of: 133 * 150 KB/s = 19,950 KB/s, which is rounded up to 20 MB/s.
Its important to note that this speed is optimal speed, which may sometimes be slow or faster depending on your camera, or other equipment, what I can assure you off, is anything slower than 133x WILL before its lifespan is over cause you to lose a potential precious memory. I try to only buy 2o0x-400x for my camera equipment, and I only really buy (in order of preference) SanDisk, Kingston, Transcend, Samsung and Pretec cards.
Memory Card Reliability
The currently used chip type which is NAND flash has an endurance of 1,000,000 writes per location, this is significantly less than magnetic media like the MicroDrive, but you should be aware that magnetic media is prone to shocks. In general if you drop a solid state memory card the odds are high the card will be fine, if you drop a magnetic drive the odds swing massively towards breaking the drive.
Memory Card Death
Its important to know how to spot a dying card, one of the most tell tail signs is before failure most cards prone to frequent errors on read. This is often manifested as grey or parts of images missing, or files showing wrong. Depending where the error is, its also possible the drive will note massive changes in side as the bad sector will show the cluster / block size, meaning 10 bad sectors can show as 10 x 512mb or more.
Some memory cards include what’s called ECC (Error Checking and Correction) and wear levelling circuitry which are both transparent to the memory card user, although it may slow data access. The ECC corrects both natural errors and some unnatural errors and is self explanatory really but the Levelling technology sounds complex and it indeed is, but its function is very simple. It basically stops the drive writing to the same sector of chip every time, it randomly chooses somewhere from the available space to write the files meaning you get many more uses than if it started at the same place every time.
