MEMORY CARD SPEED EXPLAINED

When shopping for memory cards, we tend to compare cards by the “X” speed, such as 80X, 150X, etc. But what are we measuring? The X speed is how much information the card can accept per second, also known as the write speed. A card that can accept more information per second when compared to another is referred to as being a “faster” card. X is the baseline equal to a card accepting 150KB in one second.

1X = 150KB per second
10X = 1.5MB per second
50X = 7.5MB per second
80X = 12MB per second
150X = 22.5MB per second
300X = 45MB per second

Faster cards can accept more megabytes of information per second. But just how much of an advantage is a faster card? With some cameras, there isn’t much advantage to using a faster card, while others will benefit from the high speed.

Cameras don’t capture an image and then immediately write the file to the card. Instead, the image file goes to a camera’s internal storage memory first; this memory is called a buffer. The buffer then feeds data into the memory card at a steady pace. Often a camera’s buffer is large enough to hold a significant number of image files, waiting to be saved to the memory card. Once the buffer begins to fill up, the camera slows down considerably.

The buffer is writing to the memory card at a speed that is limited by the camera design. If a camera is designed to write at a maximum 80X speed (12MB per second), the speed won’t be increased by using a memory card that’s rated at 150X. But there certainly isn’t any harm done to the camera or card by using a card that’s faster than the camera can write either.

MEMORY CARDS FOR VIDEO CLIPS
There is an advantage to using a faster card in a compact camera for capturing movies. Each movie frame is very small, usually less than 1/3 megabyte for silent video, slightly more for sound video. Most compact cameras capture movie frames at the rate of 15 or 30 frames per second. At the higher quality 30 fps rate this means the camera is capturing roughly 10MB of information per second. If the camera is not equipped with a card rated at 80X or higher, the internal buffer will soon fill up and stop the camera from capturing video. Because sound is also captured which increases the overall file size, manufacturers often recommend cards that are even faster than 80X.

WHAT ABOUT SDHC CARDS?
Secure Digital High Capacity cards are a large capacity variation of the Secure Digital card format and are physically the same size and shape. SDHC cards are available in 4GB and larger capacities and use speed class numbers to indicate the minimum write speeds, instead of the “X” ratings. In order to use SDHC cards, the camera must be designed for this format and most cameras produced in 2007 accept them. SDHC cameras, card readers and other devices are backward compatible and will also accept SD cards.

 The Secure Digital Association (SDA) defines three speed classes in order to let users identify speed and performance capabilities of SDHC cards and the host products. The speed class rating specifies a MINIMUM sustained write speed for SDHC cards.

* Class 2 = 2MB per second
* Class 4 = 4MB per second
* Class 6 = 6MB per second

 The word "minimum" is the clincher. If a card writes at 3.99999 MB/sec it’s still a class 2 card.

WHAT’S THE BEST CARD SPEED TO BUY?
To get the best match of speed and performance, check your camera manual for recommendations. In particular, look for the maximum card size your camera will accept. Check for speed recommendations so the card you buy will keep up with the camera’s write speed when recording video and other high-demand applications.