PetaPixel

Back to Basics: The Difference Between SD SDHC & SDXC, and Which is Best for You

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I will start off by saying I am partial to SanDisk memory cards, but I recently found a great write up on their website that is pretty much universal, explaining the difference between SD/SDHC/SDXC memory cards. I wanted to share this information with everyone because sometimes it can be confusing trying to figure out which SD Card is best for you.

First off you might be asking yourself, ‘What is SD?’ SD stands for Secure Digital. SDHC? Secure Digital High Capacity. And SDXC? Secure Digital eXtended Capacity. Other formats include miniSD and microSD but your DSLR will not accept these. There is no quality/security difference between these three formats. Cards labeled SDHC usually have a capacity of 4GB — 32GB. SDXC formats can be very large and expensive. For the purpose of this guide, I am going to recommend that everyone stick with SDHC format. These cards have more than enough storage, even for the most trigger-happy shutterbug.

You will see a Class 2,4,6 or 10 on SD Cards. This is the speed rating which measures maximum transfer speed for reading and writing images to and from a memory card, expressed as megabytes per second. However, video doesn’t need as big a data pipe because the video format is a smaller “fixed stream” that uses only a portion of the data pipe.

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Unlike card write speeds that measure maximum performance, class ratings measure the minimum sustained speed required for recording an even rate of video onto the card. The class rating number corresponds to the transfer rate measured in megabytes per second. Class 2 cards are designed for a minimum sustained transfer rate of 2 megabytes per second (MB/s)1, while Class 10 cards are designed for a minimum sustained transfer rate of 10MB/s2.

So what does this difference mean for you? Rated Speed (e.g. 15MB/s, 30MB/s, etc.) is maximum speed of the card and also what you would expect to approximately see in typical usage of writing or reading files on the card. This measurement is pertinent to still photography, especially for taking pictures with high-resolution and/or saving in RAW format where the files created are very large. The faster the card, the faster it can save the file and be ready to take another picture. You can really notice speed differences with high-megapixel DSLR cameras when using multi-shot burst mode.

Still digital images shot on high-megapixel cameras should utilize fast data throughput (a large data pipe), higher speed cards for improved performance. Higher speed cards can also improve how fast you can transfer the files to and from the card and your computer.

Speed Class is a minimum speed based on a worst case scenario test. The Speed Class is important for video mode or camcorders, where the device is actually saving a steady stream of data. The resolution and format of the video determines the amount of steady stream data. This translates to a minimum speed you need to guarantee that the video captured on the cards is recorded at an even, sustained rate with no dropped frames (which would result in lost data and choppy playback).

Compared to high-megapixel photography, video doesn’t need as big a data pipe because the video format is a smaller “fixed stream” that uses only a portion of the data pipe. But you do need a minimum guaranteed speed for the SDHC card that satisfies the requirement of the data stream. Your camera’s specifications should state the minimum SDHC Class Rating required.

Using a card without the proper class rating on a more advanced camera, such as a high-definition (HD) camcorder or Digital Single Lens Reflex (DSLR) camera with HD video record settings is likely to result in an error message indicating that video can only be recorded at a lower definition setting.

The current SDHC specification defines Class 2, 4, 6, 8 and 10 as follows:

minimumspeed

UHS Speed Class was introduced in 2009 by the SD Association and is designed for SDHC and SDXC memory cards. UHS utilizes a new data bus that will not work in non-UHS host devices. If you use a UHS memory card in a non-UHS host, it will default to the standard data bus and use the “Speed Class” rating instead of the “UHS Speed Class” rating. UHS memory cards have a full higher potential of recording real time broadcasts, capturing large-size HD videos and extremely high quality professional HD.

So that’s it! I hope this helps bring some understanding and knowledge so you can make the right choice the next time you are on the hunt for some new SD cards for your digital camera.


*1 1 megabyte (MB) = 1 million bytes
*2 Based on SanDisk internal testing; performance may vary depending upon host device.


About the author: Martin Moore is a photographer, traveler, filmmaker and writer based out of Milwaukee, WI. You can see his work on his website, or by following him on Twitter, Facebook and Instagram. This article originally appeared here.


 
  • http://profiles.google.com/bogorad bogorad

    Too bad these ‘ratings’ are misleading and mostly lies. As one can clearly see here

    http://www.tomshardware.com/charts/sd-cards-2014/-4-Random-Write-512-KB-MB-s,3475.html

    only the most expensive cards (top 6) even cross the 10MiB/sec threshold. And no, you never get ‘sequential write’ when shooting stills.

  • OtterMatt

    That’s (unfortunately) what happens when pretty much every memory card comes from China under multiple brands. Very few cards are actually not made by the same one or two factories or have any significant differences, no matter how they’re branded or labeled.

  • http://www.imajez.com imajez

    I would like to start by saying how much I hate Sandisk, their unreliable cards and the fact that they don’t give a crap when their ‘professional’ cards flake out on a documentary shoot losing the key footage. We had 3 Sandisk cards fail on a single 10 day shoot. A CF, an SD and a micro SD in three different cameras. I’d given up on them before that, but my colleagues were still using them. :(

  • woofa

    “I will start off by saying I am partial to SanDisk memory cards” Okay, and now you’ve exposed how little you really know.

  • OtterMatt

    All I would say is that I’ve yet to have one fail on me. Thankfully, I don’t shoot many important things.

  • woofa

    They must have had some real hand picked Sandisk Extreme Plus. The last one I benchmarked sucked and I’ve had two out of 5 fail on me. I’ve never found spending the extra or any brand I’ve tried to have any real edge over another consistently.

  • Sir Stewart Wallace

    Unfortunately for me, I’ve had two of them fail on me. I switched to Samsung’s line of cards and found them to perform as well/ better than my best Sandisk. Though, that was in SD land. Now I’m in CF land and the transfer rates are faster by far and I’ve not had a single CF card fail. They’re both Sandisk (came with the camera).

  • Rob S

    Wow so much fail here:

    “SDXC formats can be very large and expensive. For the purpose of this guide, I am going to recommend that everyone stick with SDHC format. These cards have more than enough storage, even for the most trigger-happy shutterbug.”

    Um, SDXC is almost always equal or cheaper when you figure cost PER GB. So as an example at Amazon right now I can buy a 32GB Sony Class 10 SDHC UHS1 card for $17.50. The 64GB SDXC Class 10 UHS1 card cost $35.95 – $.014 cents per GB more than and SDHC card. And $36 for 64GB is hardly expensive (I got that very card for $29 on sale).

    Any recommendation for a memory card used in a modern DLSR should come down to biggest capacity you can afford and UHS1 as a minimum. No DLSR made going forward is not going to support UHS1 with the possible exception of the absolute entry level. It is crazy not to tell people to buy a UHS1 when there is almost no price disadvantage to it. RAW files are running 20MB or more on almost every DLSR. Even a short video can easily top 200MB. Encouraging someone to buy a small card that cost the exact same on a per GB basis is crazy and bad advice. Get a 64GB card and never worry that you are going to run out of space. Get a 64MB card and if you forget to reformat after your last download its no big deal. Get a 64MB card and you reduce the number of times you potentially break off the memory card door.

    Your description and explanation is excellent but your advice is bad.

  • http://kyleclements.com/ Kyle Clements

    “Encouraging someone to buy a small card that cost the exact same on a per GB basis is crazy and bad advice. Get a 64GB card and never worry that you are going to run out of space. Get a 64MB card and if you forget to reformat after your last download its no big deal. Get a 64MB card and you reduce the number of times you potentially break off the memory card door.”

    If you are using a low-end camera with only one card slot, meaning no RAID-1 configuration, I would strongly advise *against* using the largest cards you can afford, and would recommend using multiple smaller cards.

    The fact of the matter is, cards fail, and rather than hope for the best, you should plan for the worst, and switch it up regularly.

    Would you rather lose an entire wedding, or just one portion of it?
    Would you want to lose an entire vacation’s worth of footage, or just day two’s footage?

  • Rob S

    “Would you rather lose an entire wedding, or just one portion of it?” – Low end camera and wedding? And I suppose you are going to ask the wedding to take a short break while you change cards?

    I have had 2 SD cards fail in 8 years. What is more likely – that you will have one card fail during a vacation or that you will lose one of the many cards you packed?

  • Dale Tan

    Thanks for covering the basics for SD. Will there be a similar post for CF cards? there’s a whole bunch of speeds out there, and I’m not entirely sure whether they matter or not.

    And yes, I’ve only had SanDisk SD and CF cards, and none of the dozen I have, have failed in the past 6 years. Not top performers, but they are OK for that price.

  • http://www.joshrosscreative.com/ Josh R.

    Agreed this is the standard procedure for every professional I’ve ever worked with.

  • http://www.imajez.com imajez

    The chances of any one individual having a card fail is quite small as even with a supposed 2-3% failure rate you need a to buy a lot of cards to guarantee getting a failure.
    However at least 50% of the Sandisk cards I’ve bought [from proper sources] has died, despite cards being looked after and used in many different cameras.

  • http://www.imajez.com imajez

    Not failed – yet!

  • http://www.imajez.com imajez

    Losing cards, particularly small fiddly ones is even more of an issue than card failure.
    I prefer CF because it is physically bigger, as for the minuscule micro SD cards, when they pop out of their tiny slot a bit too enthusiastically and onto the floor, nightmare.

    Not keen on the smaller card theory as being able to shoot without worrying about changing a card with a one off occasion such as a wedding or journalism is far safer.
    Plus I once had had a card bork on me when it got filled to capacity when I was shooting such an event. Data had to be recovered and I missed shots whilst changing the card too.

  • analogworm

    And why are you looking at 512Kb random write instead of sequential, which is what the class rating is about and does matter for video..

  • Carsten Schlipf

    Hm, what camera do you have? This will be a great warning to anyone buying a similar model, if changing an SD card takes longer than 3 seconds with your camera.

    In addition to the points above shooting with multiple cards allows you to continue shooting while your assistant is already downloading the files to a laptop – in the end you even have a backup of the last images.

  • Rob S

    So you go from a discussion on the BASICS of SD cards and specifically address low end cameras and then start talking about assistants and backing up during a shoot. Yeah that makes sense.

    This post was written for casual shooters and beginners, not professionals with assistants. If you are a professional with assistants and you are reading up on the difference betws SDHC and SDXC I weep for your clients.

    If you are changing an SD card in 3 seconds than you are probably keeping them in a pocket or dumping them in a bag. Me, I use a Pelican case. When I change cards I do so carefully and deliberately, making sure I take an empty card from the empty side and putting the full card, face down, on the full side. And as imajez said above, I try to never “fill” a card but instead change before filling to prevent writing to the bad sectors that every card has.

    You keep shooting small cards that you toss around after changing them in 3 seconds.

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  • Carsten Schlipf

    I can take more than 400 RAW files on a 16 GB SD Card. Well, that’s more than enough for me to not worry about space.

    Would you have had a second card on your event, you could have continued shooting with that card without missing the shots.

  • Peng Tuck Kwok

    First of all these are writes. Secondly they are random writes. SHDC never says you must fulfill XYZ MB/s for random writes. They just say writes. So manufacturers quote linear writes, which in practice is pretty much what happens when you use your camera. Look at the awesome benchmark numbers posted when you select linear writes. In fact even a home SSD that you buys is going to perform worst in random writes than linear writes.

  • Peng Tuck Kwok

    Because it’s easy to cherry pick bad results from a benchmark and draw attention to the bad things.

  • http://www.imajez.com imajez

    Do you mean second card on your camera, not event? That wouldn’t work for me as I mirror data if using two cards.
    This was IIRC near the end of a verrrrry long day’s shoot and cards I had at time were only 8GB+4GB. Not sure 16GB cards were affordable then and the 5DII didn’t have dual card slots.

  • http://profiles.google.com/bogorad bogorad

    Not really. When you record video writes are indeed (mostly) linear. But when you shoot stills it’s writing all over the place (you’ve heard of FAT, right?). So doing 512k random write tests is about right.

    Home SSDs also suffer when used in this scenario. Mine does:

    125MiB/sec 512k-reads
    82MiB/sec 512k-writes

  • http://profiles.google.com/bogorad bogorad

    Because when shooting stills it’s random. Just try shooting at the max speed of your camera and see how slow it writes. Nowhere near 10MiB/sec.

  • Peng Tuck Kwok

    You’re also quite dense.

  • Peng Tuck Kwok

    I’m saying you’re just cherry picking numbers and calling them out as bad simply because you can. Anyone knows random reads and writes will always be poor and disk manufacturers usually post sequential results.

  • http://profiles.google.com/bogorad bogorad

    Oh, how nice of you to say that!

  • Peng Tuck Kwok

    Thank you. Keep cherry picking results from a benchmark and posting them as ‘news’.

  • Ken Elliott

    Same thing here. I’ve been a long term fan of Sandisk, but the SD cards have been very disappointing. My camcorders don’t like them, yet they love Transcend cards, which perform much better at half the price.

  • Ken Elliott

    >>”However, video doesn’t need as big a data pipe because the video format is a smaller “fixed stream” that uses only a portion of the data pipe.”

    Sorry, but you lost me right there. Still cameras can buffer their shots, and thus work fine with rather slow cards. Video cameras deliver a continuous stream, and cannot buffer for very long (if at all). So slow cards won’t work at all with video, while they will work with stills.

    Next, the “Class rating” is for recording, not read/write (per the SD Card standard). https://www.sdcard.org/consumers/speed/speed_class/

    I appreciate that you are trying to do a good thing by sharing information, but some of the data is inaccurate, wrong, or simply copy-paste from Sandisk’s web site. We are not bashing you – we are bashing the SD card industry, which has been far too confusing with regard to card speeds.

  • ninpou_kobanashi

    I’ve never had one fail, ever. I wonder if folks are buying the counterfeit versions? Fake versions are being sold on Amazon. SD even published a guide to detect the fake ones.

  • http://www.imajez.com imajez

    So how many hundred cards have you bought then?
    I’ve had failures with cards from major camera shops who get supplied direct from importers and I do not buy from eBay

  • ninpou_kobanashi

    I think I’m on like my 8th card? Just saying. BTW, Amazon re-sellers were selling fakes, like I said earlier, so it’s not like you have to go to the sewers (eBay) to be affected.

  • http://www.imajez.com imajez

    Uh, did I say I bought from Amazon? No I said major camera stores.
    8 cards is still a low amount so you are very unlikely to experience failure.

  • http://www.korioi.net/ Korios

    I do not think that’s the case with video. Video requires a much higher bit rate. The author is mistaken on this.

  • yorgo

    simple, concise and to the point. thanks.

  • David Halfpenny

    You’ve muddled bits, bytes and Baud.

    It’s not entirely your fault – a lot of the people you’ve cribbed from do, and even the SD association uses the non-existent unit MB/s.

    But if you’re writing Back to Basics you should take your own advice rather than cut’n’paste other peoples typos :-)

  • Hhh

    What educated person you are. MB stands for megabits not megabytes. Lol