SD Cards Explained | Ask David Bergman

Today's question from Clark A. is, "I need to buy a new SD card for my camera, but there are way too many options. Can you explain what all the numbers mean and let me know which one to buy?"

00:00 Intro
00:40 Different types of memory cards
01:49 Different types of SD cards
02:40 Card Capacity
03:12 SD, SDHC, SCXC, and SDUC
04:29 Backwards compatibility
05:22 Read and write speed
07:11 Speed class
09:31 Bus speed class
10:18 Prograde Refresh Pro
11:06 Most important SD card specs

→ Article:
Picking the Right SD Card: What Do the Numbers Mean?

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THANKS SO MUCH FOR WATCHING!

[jpdj]

Great overview. And, yes, there is wear each time you cause a rewrite of a memory cell. The card has its own controller that runs firmware and this implements a process called "wear leveling". Imagine a card that can hold 1, 000 stills of your camera, but you shoot 100, on a portrait session. You copy the shots to your workstation for postprocessing and maybe to a backup system. Now when you "format" the card, these hundred are not erased. Instead they are made invisible in the outward facing administration of what files are on the card. You next session with 100 shots is stored after the first 100 and the story is repeated.
Once all the blocks (a block is a range of memory cells) in the card have been used, the wear leveling will erase-write to the blocks used first.
Each of these rewrites is done at a higher voltage than is nice to the card's tech and this is the wear. Think "brownout" not "blackout".
How many times this can be safely repeated depends on the quality of the memory cells. Cheaper cells can sustain less rewrites. In general. Write speed also plays a role in price.
In enterprise SSD storage we see manufacturers place more GB than advertised. This is called over-provisioning and it is also applied to memory cards. Cheaper memory cells and 50% over-provisioning is cheaper than much more robust memory cells.
For a long time, with SSD, the wear a device can sustain is expressed in TBW - total bytes written. If we look at the TBW of a certain generation of Samsung "EVO" SSD and compare them with the "PRO" of that generation, we see that (TBW/capacity) and EVO SSD can sustain 300 rewrites and a PRO 3, 000. That's a dramatic difference.
Over-provisioned capacity is available to wear-leveling not to the operating system and the user.
What we see today is that card manufacturers who have been on the cheap cells with over-provisioning track have learnt that they got no or little complaints about cards failing. What they are doing is adding half of the over-provisioning to the capacity on the label and raise the price bit. The card looks cheaper in $/GB but actually is a lot more expensive.
I asked one manufacturer for their TBW number with a certain card and they answered "enough". That felt like getting the middle finger. When I asked Delkin, they answered politely, in depth, and I can wholeheartedly recommend their "Black" CFexpress Type B cards. But, I would always stay with the standard capacities of 128, 256, 512, etc.

The second elephant in the room is guaranteed minimum sustained sequential write speed. The W and R speeds on the label of a card are maximum speeds and you may need a special card reader to be able to come close. As these cards can be very fast for a shot time and next fall back in performance, we must assume they have an extremely fast cache memory into which incoming data is stored and that next is moved to slower memory cells by the controller. In a HDD (hard drive with magnetic platter) that slower speed is the "media speed" and is dramatically lower than the I/O interface-controller-cache speed. "We" use RAID 0 arrays to work around that by having so many parallel drives that you never hit the media speed.
Some memory card series become faster when there is more capacity in them and this suggests these cards actually work like a RAID 0 array internally.
Other cards have faster cells and potentially better TBW and hence are more expensive. The problem is to find this out. And know what we pay for - real substance or thin air.

Are these TBW and sustained minimum sequential speed important?

Well, if you fill your card every day completely, then a card with 300 rewrites is done in 300 days or sooner.
The controller maintains an administration of the times a block is used and when a card with 300 rewrites has one block that has had 300 rewrites, then that block is marked unavailable. Rewrite every day and after 300 days it stops.
This is why one influencer buys the cheapest cards and never rewrites them. He presumes that his data will last in that card forever.
And that's another elephant in the room. Ask how long data is safe in a card that is not powered - to people with degrees in electronics and quantum physics - and you'll find that the answer is "between 7 and 7, 000 hours".
Here it is very important that the card has a protection system for data integrity so a spontaneous bit-flip can be corrected correctly. Spontaneous bit-flips are a thing and these happen in magnetic layers too. RAID 0 protects against nothing, RAID 1 protects against the loss of a drive, but has no integrity checks, RAID 5 has serious data integrity potential.
As David mentions, Prograde has n application to inspect card health and basically this could be a program that readds the card's controller administration to see how many rewrites the card can sustain and how many have been used. If it is smarter than that then it can do data scrubbing where the integrity of each byte of data is verified and if necessary repaired - provided the card has some integrity mechanism (like ECC).
Sony has an app for some of their "Tough" cards and I have those, with the Sony card reader, but the app has worked once, ages ago and now I use a third party freeware app (CrystalDiskInfo IIRC).

If you shoot video then yes, at 4K or 8K the minimum guaranteed sustained sequential speed is very important for you. If you shoot many takes a day with multiple cameras then a movie house may want fast sustained read speeds as well, in order to get the "takes" into the editing infrastructure a.s.a.p. - so they can be watched on a larger display or in projection.
And we now see cards that - in CFexpress Type B format - are so fast that the camera's buffer never fills even at the highest stills frame rate at maximum resolution.

While this video is about SD cards, and I mention CFexpress Type B, people may complain these CFe cards are so expensive. Well, they are as expensive as top SD UHS-II cards but much and much faster for the same price.

Finally, I would also look at the supported/guaranteed operating temperature range. Look at Morten Hilmer shooting nature in the freezing cold of Svalbard (in the arctic circle) or in the winter of Norway when a polar wind blows around and temperature has dropped to -20C (-4F). Most cards are guaranteed down to -10C (14F).

As David (re. SD cards) mentions UHS-I with one row of contacts versus UHS-II with two rows of contacts for higher speeds, we have to know that while UHS-II cards are compatible with UHS-I devices they can never reach the speed on their own label over a UHS-I interface. And while that may seem obvious, we have to know that running these cards over a UHS-I interface will not be as fast as fast UHS-I cards can be (there may be exceptions of UHS-II cards being as fast as UHS-I in a UHS-I device, but I don't know them).

[larrylanggard]

Thanks! Halfway through, I thought my head would explode, but by the end, I think I got it. Very compact explanation of a topic I barely understood before. Well done!

[GOAP]

12:27 and then Canon released the 50 frame burst @ 195 fps with full raw+jpeg feature on the R3... and I was glad to have Prograde V90 cards for the SD slot.

[Sportserjeff]

Well said now I'm going to watch this again and take notes. Mostly I just looked at class 10 and size when I shoot models I try to only take 500 photos because next comes editing!

[InfectedChris]

Glad you mentioned the Zoom H4n Pro because it's what I use for my podcast and it's great!

[RickLincoln]

Long video with a lot of data...and worth every moment that I spent watching it. Very informative!

[ChaitanyaShukla]

bit/sec(b/s) is used to define bandwidth of an interface while Bytes/sec(B/s) is used for maximum read or write capabilities of a storage device.

[Analisem]

Complete yet concise as always. Thank you!

[mikedoiron]

Thanks David. Well explained and laid out. Answered a lot of my questions.

[sfogel]

Thanks for this comprehensive info! I took a screenshot of the chart. Very handy.

[hersh]

This was a LOT of information but a lot of incredibly useful information! This makes me want to look at the SD cards I have and check out the info on them!

[alexanderpons]

Great video and now we know, thank you David Bergman!

[PeteTaylorPTI]

I've run SD and Compact Flash (yeah, the ol') through the washer and dryer before with no issues. LOL

[s.cottrill]

This was extremely informative and answered all my questions about what the little numbers and symbols stand for

[klburt]

This was INCREDIBLY helpful. Thanks so much!

[charlesdavis]

great details - always enjoy David's videos

[brad_in_yyc]

I wonder if Sony Tough cards or Angelbird have something similar to that Refresh Pro that Prograde offers. Great detail in that video David. Thank you.

[wayneking]

Great video. Well explained and well organized. Look forward to future videos.

[JDFloyd]

Any news about when the major manufacturers will release 2tb SDXC / SDUC cards?

[sabelosibisi]

This was unbelievably helpful! Thank you!