32gb or 64gb?

[Rick Law]

Now that my stock of 32gb micro SD cards are used up, I'm thinking of switching to 64gb.  I have a few card readers and a few micro-SD to standard-SD adapters, exactly like the pair shown in the picture.  Not so much the expense of getting the new readers/adapters, but I want to avoid confusion for myself if I have to juggle 32gb and 64gb adapters/readers.

Before I order a pack, I like to pick your brains to clarify if my understanding is correct...  thanks

Question 1:
My understanding is that the MicroSD to StandardSD adapter is purely electrical, MicroSD pins to Standard SD pins in the adapter and therefore "size insensitive".  The adapter that that works for 32gb should work just fine for 64gb.  Am I correct?

Question 2:
Since the CHS limit is around 8gb, these card readers are using LBA.  I know there is an LBA limit around 128gb.  Am I safe to assume that "high probability" the 32gb card readers should work fine with 64gb SD?

Thanks guys for sharing your experience...

[AntiProtonBoy]

Answer 1: Yes, correct.

Answer 2: I used 256 GB in shitty card readers without any issues. Most modern devices reading SD cards should support upwards of 1 TB (for example Raspberry Pi 4).

[RoGeorge]

Some devices can not read cards bigger than 32 GB (my mobile phone can not), same as some devices can not read cards bigger than 2 GB.

You should check first with the product's manual, or with the manufacturer.  Ideal, test before you buy, especially when buying expensive high speed cards.

[golden_labels]

All SD slots should be able to read and write SDXC cards. While there were some issues with early devices, that shouldn’t apply to you, as your reader is already known to handle 32G cards.

However, being able to access a card is not the same as being able to access the filesystem on that card. SDXC cards are normally using the exFAT filesystem. You should make sure that each operating system you use can handle exFAT or you will have to format the card as FAT32. Until 2018 in order to access your data on an SDXC card, you were obligated to buy a product from a Microsoft-led oligopoly or rely on potentially illegal and unstable implementations. So many pre-2019 devices are likely to not be able to access exFAT-formatted SDXC card even if the reader is theoretically supporting 64GB media.

The easiest way to check is to see what filesystem are your 32GB cards using. If it’s exFAT and you experienced no issues, everything should be fine with 64GB cards too.

[Rick Law]

...
However, being able to access a card is not the same as being able to access the filesystem on that card. SDXC cards are normally using the exFAT filesystem. You should make sure that each operating system you use can handle exFAT or you will have to format the card as FAT32. Until 2018 in order to access your data on an SDXC card, you were obligated to buy a product from a Microsoft-led oligopoly or rely on potentially illegal and unstable implementations. So many pre-2019 devices are likely to not be able to access exFAT-formatted SDXC card even if the reader is theoretically supporting 64GB media.
...

Good point.  All my PC & Laptop are exFAT able, but I have not verify my other devices (such as my Andriod TV boxes).

Instead of ordering a 5-pack, I will start with 1.  Now that I know the Micro-SD to Standard-SD adapter(s) will work, the one 64gb card wont go to waste even if my other devices wont work with it.  At least I can use that for my laptop.  This gives me a perfect excuse to have one higher rated U3 card to see how well it actually does comparing to the U1's I have, and to test which of my other devices work with it, or not.

Thanks, guys for all your helpful replies.  The knowledge you all so generously shared is much appreciated.

[David Hess]

Some devices can not read cards bigger than 32 GB (my mobile phone can not), same as some devices can not read cards bigger than 2 GB.

You should check first with the product's manual, or with the manufacturer.  Ideal, test before you buy, especially when buying expensive high speed cards.

My old GPS will not work with cards larger than 2 GB but I found a workaround.  If I partition a larger than 2 GB SDXC card with a partition of 2 GB or less, then it will work fine because accesses are limited to the first 2 GB.

[Rick Law]

Some devices can not read cards bigger than 32 GB (my mobile phone can not), same as some devices can not read cards bigger than 2 GB.

You should check first with the product's manual, or with the manufacturer.  Ideal, test before you buy, especially when buying expensive high speed cards.

My old GPS will not work with cards larger than 2 GB but I found a workaround.  If I partition a larger than 2 GB SDXC card with a partition of 2 GB or less, then it will work fine because accesses are limited to the first 2 GB.

Interesting...  I am still using my Treo650 (for a game I like).  Palm (the manufacturer) specs say 2GB limit on the SD card.  Just before SDXC became standard, I found a 4GB SD card that works and the Treo access all 4GB just fine.

With your success in re-partitioning the SD for your GPS, I will experiment (after I migrate to 64gb cards and have some 32gb SD cards free up) and see if I can give the Treo a larger brain just for the fun of it.

[Berni]

Electrically all SD cards are the same thing, only difference is that some of the new cards also support optional DDR clocked high speed modes and lower operating voltages.

Most of the incompatibility comes from the software reading the card. Generally anything under 1 GB will work anywhere but then there are various common barriers:
- SD card with 512byte sectors gives 2GB max. It is the limit if SDHC or SDXC cards are not supported
- FAT16 filesystem can only do partitions of 2GB max. If FAT32 and others are unsupported this is the limit.
- SD cards with 1024 or 2028 byte sectors can reach 4GB or 8GB. Some devices freak out when they see non 512 byte sectors and not work
- SDHC cards are supported to higher capacities by a patch to the interface protocol to allow larger addresses. This allows 4GB 8GB and up cards without weird sector sizes Older devices might not know how to speak the new protocol
- SDXC cards are once again updated to support up to 2TB of addressable space, same as SDHC older devices might not support it, but is i think compatible with SDHC.

But in general once we have gotten past 8GB things are solved for some time. If a device supports a 16GB card this means it must at least support FAT32 and SDHC cards so the limit is effectively 2TB unless something goes wrong in the firmware.

[David Hess]

My old GPS will not work with cards larger than 2 GB but I found a workaround.  If I partition a larger than 2 GB SDXC card with a partition of 2 GB or less, then it will work fine because accesses are limited to the first 2 GB.

Interesting...  I am still using my Treo650 (for a game I like).  Palm (the manufacturer) specs say 2GB limit on the SD card.  Just before SDXC became standard, I found a 4GB SD card that works and the Treo access all 4GB just fine.

With your success in re-partitioning the SD for your GPS, I will experiment (after I migrate to 64gb cards and have some 32gb SD cards free up) and see if I can give the Treo a larger brain just for the fun of it.

As Berni points out, the problem is with older devices not properly addressing the card to access data above 2GB.  Creating a 2GB partition avoids this problem because it prevents accesses above 2GB.

[amyk]

- FAT16 filesystem can only do partitions of 2GB max. If FAT32 and others are unsupported this is the limit.

You can get to 4GB with FAT16 if you use 64K clusters, but some devices may get confused.

[magic]

Lots of confusion here.
There are 4 generations:

SD(SC)
The original standard, retrospectively named "standard capacity". Card capacity up to 4GB can be encoded and the officially supported filesystem is FAT16. Some implementations of FAT16 may not understand 64KB clusters and therefore 4GB FAT16 volumes. The same devices may or may not support FAT32 - this was never required by SD, but could be part of the embedded OS they use.
The subsequent SDHC standard forbade 4GB capacity cards and required them to be SDHC instead, but rare 4GB SDSC cards exist.

SDHC
A new standard introduced in 2006 and implemented by most devices since then. The Card Specific Data register layout has been modified to encode large capacities (but only 32GB is permitted by the standard) and version number increased. Pre-2006 devices refuse to read such cards and if they attempted anyway, they would decode the capacity completely wrong. New commands have been added too and SDHC hosts issue at least some of them to all cards but SDSC cards reject them. The official filesystem is FAT32 but many devices will work with FAT16 on a sufficiently small partition.
Rare 4GB cards exist that are dual-mode. They watch the commands issued by the host and present a 4GB SDSC CSD to SDSC hosts and a 4GB SDHC CSD to SDHC hosts.
Because SDHC forbids 4GB SDSC cards, some pedantic SDHC hosts may reject a 4GB SDSC card. I think I have owned one such device, but I sold it so can't confirm.
Because SDHC forbids 64GB+ cards, some pedantic SDHC hosts could reject SDXC cards.

SDXC
Introduced in 2009, mostly same thing as SDHC, but cards 64GB+ are permitted and mandated to use exFAT.
Some SDXC hosts (Panasonic, I'm looking at you) actually enforce this and refuse to read FAT32 formatted SDXC cards, others don't give a damn.
FAT32 formatted SDXC cards generally work in SDHC hosts, but I have encountered issues with excessive memory use on such filesystems. It helped to increase cluster size, thus reducing cluster count.

SDUC
Some 2018 thing I'm not familiar with.

Then there is a completely orthogonal issue of interface speeds which have been added over the time. AFAIK, all cards and hosts support some lowest common denominator SDSC speeds and can figure out the highest speed supported by both peers. Never had problems with that.

Using a 2GB partition can only solve filesystem compatibility problems - presumably lack of FAT32 support. It will not enable a pre-2006 device to work with SDHC or SDXC.

Question 1:
My understanding is that the MicroSD to StandardSD adapter is purely electrical, MicroSD pins to Standard SD pins in the adapter and therefore "size insensitive".  The adapter that that works for 32gb should work just fine for 64gb.  Am I correct?

Question 2:
Since the CHS limit is around 8gb, these card readers are using LBA.  I know there is an LBA limit around 128gb.  Am I safe to assume that "high probability" the 32gb card readers should work fine with 64gb SD?

Adapters are dumb and SD cards have their own sector addressing schemes which differ between SDSC/SDHC. CHS/LBA only comes to play when an SD card is used to emulate a magnetic disk, for example by plugging it into a USB Mass Storage type reader. Problems are unlikely to arise in practice because software that supports USB tends to support LBA too. I imagine there could be issues if you attempt to boot DOS from such card reader.

USB SD card readers come in two flavors. Some are pure SD hosts and the software needs to know how to talk SD and tell the card reader what commands to issue to the card. Others handle SD internally and appear as generic USB Mass Storage devices.
The former type will work with every card, the latter will not work with SDHC/SDXC if it was made before 2006. In principle, SDHC readers ought to work with SDXC because the difference is filesystem (handled by the OS) and an artificial capacity cap imposed by the earlier standard.

[RoGeorge]

There was a 2GB limitation at first.  I think that one was a hardware limitation, because old SD-card readers won't see and won't work with any card bigger than 2GB, even when the card is not yet formatted.  I have two of those old USB card readers and they both fail to work with bigger cards.  That behavior seems file system agnostic, so I'll assume is a hardware limitation.

[magic]

It's a difference in SD card metadata registers. You tell me if it's "hardware" or "software".
In principle, such devices could support SDHC with a firmware update but generally no such updates have been provided.

If you can find a 4GB SDSC or dual-mode card, it may work too. At least old Canon cameras supported such cards.

[Doctorandus_P]

Every few years the stretch the limits of SD cards a bit.

I assume "they" do it to make as many gadgets as possible obsolete because they are not compatible whith the "newest" yet to be invented "standard".

A bit like USB, where "they" invented a very limited 16 bit address space with the intent of selling simple numbers for a lot of money.

It's what happens you let commercial companies set "standards".

[Rick Law]

Thanks to all your contributions, I learned a lot more knowledge of SD cards, SD formats, readers, and adapters than I expected.  Very interesting indeed.

Following up on a couple of items:

(a)  With this discussion, my interest in my old Treo650's 4gb SD was renewed and said on a replied I would check on it to see how it manage >2gb SD.  I found out that my Treo650's 4gb card is actually just FAT32 with 64k clusters and no other magic.  Initially, that 4GB SD at the time was so hard to find as most >2GB switched to SDHC/SDXC cards.  I thought it was some other magic...

(b)  With knowledge from this thread that I don't need to purchase additional adapters/readers, I purchased a SanDisk Exteme U3 64GB to test.  Only 1/2 my devices' SD slot works with 64gb.  So, the attractiveness of 64GB is limited to me at this time...  I think for now I would stick with 32gb as my main SD cards for misc application.