Sounds incorrect. SD cards can't be 4GB, and a device that doesn't support 4GB cards isn't a SDHC device.

There might have been manufacturers that disregarded specifications, but I doubt those were common.

There were some manufacturers that did disregard the specifications. I recall many people asking about specific brands and cards for camera's and old school MP3 players and there were quite some offerings. Still available it seems: https://www.memoryx.com/ts4gsdc.html

I've got one of those Transcend 4GB cards, it operates in both SD (byte addressing) and SDHC (sector addressing) modes depending on how it's initialized.

Oh they are sort of common? SD card compatibility is even more of a mess than I thought it was? Wow.

2 and 4GB SD cards are strange. You'll have to use software that will report and describe a card's CSD registers. There's probably a few for each OS. That will let you know what to predict when trying it in an older device.

https://en.wikipedia.org/wiki/SD_card#SDSC_cards_above_1_GB

- 12-bit storage for memory cluster count (max 4096) "C_SIZE"
- 3-bit storage for blocks per cluster (4, 8, 16, 32, 64, 128, 256, 512) "C_SIZE_MULT"
- SD v1.00 assumed 512 bytes/block: 4096 * 512 * 512 = 1GB "READ_BL_LEN"
- SD v1.01 a 4-bit field indicated 1024 or 2048 bytes per block: 4096 * 512 * 2048 = 4GB
- Two bits that were formerly reserved now identify the card family: 0 is SDSC; 1 is SDHC or SDXC; 2 and 3 are reserved.
- Because of these redefinitions, older host devices do not correctly identify SDHC or SDXC cards nor their correct capacity.

Those details don't really matter; SDHC cards require an extra initialisation command that non-SDHC devices don't know how to do.

Hi, quick update.
There's a new article at hackaday.com that covers this issue. 😀

https://hackaday.com/2020/09/08/size-does-mat … es-to-sd-cards/

Not a very good article, has several factual inaccuracies.

It also misses to mention MMC (Multi Media Card).

Anyway, it does at least "bring some light into the dark". 🙂
For example, I didn't know of the 1GB barrier. Or that FAT16/FAT32 can be used to trick devices into accepting unsupported cards.

Edit: Several edits. My smartphone does sabotage every sentence. 🙁

That's because there is no 1GB barrier. The actual block length was always 512 bytes, the field in the CSD was only ever used to calculate the capacity. It made no difference to existing hardware because non-SDHC cards use byte-addressing, not sector/LBA addressing.