Digital Media Cards Are Not All Created Equal

Posted Oct. 31st, 2012 by Daniel J. Cox

A few months back I had the good fortune to meet  Peter Liebmann from SanDisk. We met on the Mentor Series Oregon Trek and during a couple of lengthy bus rides he shared with me and all the Trekkers great information about digital media cards. I was so impressed with his off the cuff program I asked him if he would be interested in writing it all out so I could offer it to my readers. So below is what Peter sent me to add to this blog. It’s great information and after using an off brand card that developed issues, I was even more interested in what Peter had to say. I think you will to. Thanks Peter for putting this all together.

The Concept by Peter Liebmann of SanDisk

Think about a memory card as if it is a sponge. The data from your camera is a glass of water. Three basic principles govern the relationship between the sponge (card) and the water (data).

Card capacity – how much water (data) can the sponge absorb

Write speed of the card – how quickly can the sponge (card) absorb the water (data), expressed in MBS (MegaBytes per Second)

Read speed of the card – how quickly can I wring out the sponge (card) once it’s full of water (data), also expressed in MBS (MegaBytes per Second)

Common Misperceptions

1. All cards are created equal

False. SanDisk is one only of six prime manufacturers of flash memory wafers in the world, and we are the leader in flash memory cards. In addition to manufacturing our own flash, we also manufacture our own controllers (the “traffic cop” under the hood that determines where data gets written on the flash). Our controller technology reduces the likelihood that any one sector wears out prematurely, so the life of the card is maximized, and bottom line – you come home with your pictures and/ or video content. We also write the code that allows all the components to communicate and we do our own assembly and rigorous quality control testing. This is not the case with some other brands of flash cards on the market

2. Class is relevant to all performance in all types of memory cards – both for still and video.

False. There are a few measurements of speed for flash cards, just like you can measure the speed of a car in both miles per hour and kilometers per hour. There are two measures of speed for CompactFlash cards – MBS (megabytes per second) and the “X” factor.

Example: Our Extreme CompactFlash cards are both 60MBS and 400X. These numbers represent the rate at which data can be transferred from/ to the card and host device (camera/ camcorder). If you know the MBS number (in this case 60MBS), you simply divide that number by .15, so in this case:

60MBS/ .15 = 400X
Conversely, if you know the “X factor, you can easily calculate the MBS: 400X x .15 = 60MBS

It’s a little more complicated with SDHC cards where there are three measures of speed. Let’s take an Extreme 30MBS, 200X, Class 6 card as an example. The same relationship between MBS (megabytes per second) and the “X” factor applies to SDHC as to CompactFlash:

30MBS/ .15 = 200X

In addition to the MBS and “X” factor, SDHC cards are also designated with a Class rating (typically Class 4, 6, or 10). The Class rating system is ONLY relevant when shooting full 1080P HD video onto SDHC cards. It is not applicable to CompactFlash cards and is NOT relevant to still photography whatsoever. By definition, Class is the MINIMUM sustained read/ write speed of an SDHC card expressed in MegaBytes per Second (or MBS). The Class system was developed when flash based video came into vogue a few years ago, as a means to ensure the end result would be a drop-out free video when viewed on a television or PC.

For example, your camera manual specs a Class 6 card for shooting 1080P video This means you need a card with a minimum sustained write speed of 6MBS (megabytes per second) to ensure proper video quality from your camera/ camcorder.

In addition, the Class rating is the MINIMUM video recording speed of the card, not the maximum performance (speed) of the card. SanDisk Extreme SDHC cards (ideal for video and still photography) run at a MINIMUM of 6MBS for video recording, and a MAXIMUM of 20MBS for burst shooting. Bottom line – not all Class 6 cards are created equal and the Class rating is only relevant to SDHC cards and only applicable to shooting 1080P HD video.

3. The speed of a card is more important when shooting video vs. still photography.

False. When recording video, you are shooting a small, but sustained stream of data onto a card (a garden hose). When you are shooting RAW files (still photography) at a burst rate of 5 or 6FPS, you are sending a 10 – 20 megabyte file (based on your particular camera brand/ model) onto a card 5 or 6 times per second (like aiming a fire hose at your memory card).

4. CompactFlash cards are “professional” and more durable than SD cards.

False. CompactFlash was the first form factor to the market and was the mainstay in digital photography for about 5 years. SD cards were developed to allow more compact camera designs, but they are actually more durable than CompactFlash cards because they are truly waterproof, shockproof, magnet and x-ray proof*.

5. SDXC cards are faster than SDHC cards.

False. By definition, SDXC is simply a measure of a cards’s CAPACITY, not speed. 0 – 2 gigabytes = SD Card
2+ – 32 gigabytes = SDHC Card
32+ gigabytes = SDXC Card
SDXC cards are NOT backwards compatible

*Up to 32GB capacity (refer to http://www.sandisk.com/about-sandisk/proof)

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There are 3 comments on this post…
  1. Portrait of Christine Crosby

    Christine CrosbyOn Nov. 6th, 2012

    Thanks Dan. I thought that’s how I understood what you had said on one of the recent trips but just wanted to be sure I was really understanding the real gist of the whole thing. I have just purchased a new SanDisk Extreme Pro 96mbs card and am excited to try it out in an action setup especially.

  2. Portrait of Christine Crosby

    Christine CrosbyOn Oct. 31st, 2012

    Thanks Dan. This helps a lot. I still have a rookie question. When you “run into the buffer” is that determined by the Write/read speed of the card or it the ability of the camera to read/write the data onto the card?? Hope that makes sense. Just wondering if I get a super fast read/write SDHC card, does the camera model (ie. my Nikon D7000 set at CH or Continuous High) effect my ability to keep shooting in a rapid action sequence or is it all about the card itself?

    Thanks!!

    • Portrait of Daniel J. Cox

      danieljcoxOn Oct. 31st, 2012

      Great Question Christine. I actually had buffer issues with the Nikon D7000 myself. D7000’s were my main cameras until recently. I switched to a SanDisk 96MBS SD card and it help immensely. A fast card is your biggest asset when you have a camera with a small buffer such as the Nikon D7000. The question about the speed of the camera writing to the buffer is a good one that’ I’m unsure of. I’ll do some digging and find out if that’s a factor. If it is I’m confident it’s not as big a factor as the speed of the card the camera is writing to. I can tell you from first hand experience that the faster, 96mbs SanDisk SD card is a big plus.

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