
Understanding Memory Cards - emptybits
https://photographylife.com/understanding-memory-cards
======
verall
This is an extremely verbose article, but for most people I would highlight
the most important things (for SD cards at least):

Buy a real brand: people have there own opinions on this, but to me this means
Sandisk, Samsung or Verbatim. Had a bad experience with Lexar once but as
always ymmv.

Buy from a real retailer: this means B&H or Adorama or a not-shady brick and
mortar store. Amazon will happily ship you counterfeit cards that will crapp
out when you need them most, like ebay will. This is coming from someone that
chooses to buy a ton of their electronics from ebay, Aliexpress or street
hawkers.

~~~
vardump
> Buy a real brand: people have there own opinions on this, but to me this
> means Sandisk, Samsung or Verbatim. Had a bad experience with Lexar once but
> as always ymmv.

I've had always bad luck with Sandisk, both CF and SD/microSD cards.

~~~
dkdklk
Buying from Amazon? You’re likely getting fakes. Genuine SanDisk memory cards
are top notch.

Sure every brand will have lemons, but if you’re seeing consistently bad
“SanDisk” cards.. you are pretty certainly not getting genuine product. Find a
reputable supplier (which is absolutely not Amazon)

~~~
jagger27
The general advice for buying off Amazon it to make sure that it's actually
coming from Amazon.com, not CheapMemoryAmerica1999.

~~~
maverick2007
From what I understand, Amazon comingles their own inventory with third party
sellers so although the cards they buy might be legit, you're not necessarily
guaranteed to get what they bought vs what CheapMemoryAmerica1999 contributed
even if you buy the ones from Amazon

~~~
jagger27
I read that as well. But Amazon does have a good return policy with respect to
that, and if you read recent reviews it seems like the problem is mostly over.

------
TazeTSchnitzel
I am surprised they didn't mention that microSD and SD cards are electrically
compatible and have passive adaptors. If you want to write a comprehensive
guide, that's a useful thing to tell people.

------
Sharlin
It’s such a ridiculous dark pattern to only advertise read speed when in
almost all cases write speed matters more. Also, the SD speed class notation
is almost totally obsolete and anachronistic because these days even the
fastest class 10 has a minimum speed requirement so low it tells you almost
nothing about the card’s performance.

~~~
gruez
> Also, the SD speed class notation is almost totally obsolete and
> anachronistic because these days even the fastest class 10 has a minimum
> speed requirement so low it tells you almost nothing about the card’s
> performance.

There are higher speed classes past class 10.

[https://en.wikipedia.org/wiki/SD_card#Class](https://en.wikipedia.org/wiki/SD_card#Class)

~~~
khedoros1
Not in the sense of a "C" surrounding a larger number than 10. Instead, you
get a card marked with all of "C10", "U3", "A2", "V60", or some crap like
that.

Give me 4 numbers: Read and write speeds, each in terms of minimum sustained
transfer rate and minimum random IOPS.

------
userbinator
Odd to see such a long article with no mention of MMC, TF, or xD.

Also worth noting that these cards (with the exception of xD, which is just a
packaged raw NAND flash) have a complete embedded system in them too:
[https://www.bunniestudios.com/blog/?p=3554](https://www.bunniestudios.com/blog/?p=3554)

------
CarVac
Unfortunately it hasn't updated anything for almost a year, but
cameramemoryspeed was always my go-to for actual speed tests of card/camera
combos.

[https://www.cameramemoryspeed.com/](https://www.cameramemoryspeed.com/)

------
Const-me
I wonder which of them, if any, contain a controller chip that does wear
leveling? All PC SSDs have them, even very small ones like M.2 2230.

~~~
pmorici
They all do. It isn't always a discrete chip though. Like in the case of a
MicroSD the memory and controller is all integrated. You can open up some full
size SD cards though and the memory and controller will be separate chips.

------
ungzd
Is there any real difference between SD, SDHC and SDXC, aside "SD uses FAT,
SDHC uses FAT32, SDXC uses ExFat"? These cards does not have filesystem
controller on it, it's not "FTP over wire", it's block-based storage device.
If I format ancient SD from early 2000s with exFat, will it become SDXC?

From Wikipedia (marked with "Citation needed"):

> The SDHC format, announced in January 2006, brought improvements such as 32
> GB storage capacity and mandatory support for FAT32 filesystems.

How dumb storage device can refuse to support FAT32?

Fun fact: SD cards support SPI interface and can be easily connected to cheap
microcontrollers.

~~~
duskwuff
SD and SDHC differ in some material ways. SD uses byte-level addressing and is
limited to a size of 2 GB. (The spec could theoretically support 4 GB, but is
limited by spec to half that, possibly as a hedge against implementation
errors.) SDHC uses sector-level addressing, lifting that limit to a
theoretical 2 TB.

SDHC and SDXC are identical at a protocol level.

------
peterburkimsher
bunnie wrote a great article about fake MicroSD cards back in 2010:

[https://www.bunniestudios.com/blog/?page_id=1022](https://www.bunniestudios.com/blog/?page_id=1022)

~~~
rasz
there is also this blackhat 2018 talk 'Reversing a Japanese Wireless SD Card -
From Zero to Code Execution'
[https://www.youtube.com/watch?v=tA7GW9XkXBU](https://www.youtube.com/watch?v=tA7GW9XkXBU)

