What is an SDHC-only device?
An SDHC-only device is a camera, card reader, GPS unit, older laptop slot or other host that supports cards up to the SDHC standard but not SDXC. Despite the name, it isn't limited to SDHC cards: SD hosts are backward compatible, so it also accepts original SD cards. What it can't reliably use is an SDXC card (over 32 GB). Its firmware wasn't designed for cards that large, and SDXC cards come formatted with exFAT, a file system many older devices can't read.
SD capacity standards
| Card type | Capacity | Standard file system | Works in an SDHC host? |
|---|---|---|---|
| SD (SDSC) | Up to 2 GB | FAT16 (FAT12 on very small cards) | Yes |
| SDHC | Over 2 GB to 32 GB | FAT32 | Yes |
| SDXC | Over 32 GB to 2 TB | exFAT | No |
| SDUC | Over 2 TB to 128 TB | exFAT | No |
The same rules apply to microSD, microSDHC and microSDXC. Compatibility only goes backward: an SDXC host also takes SDHC and SD cards, but an SDHC host can't use SDXC, and an original SD-only host can't use SDHC.
Symptoms of an SDXC card in an SDHC-only device
- The card isn't detected, or the device reports a card error.
- The device says the card is unformatted or asks to format it, because it can't read exFAT.
- A card reader shows no media, while the same card works in another reader.
Don't accept a format prompt if the card holds data you need: formatting erases the card. Copy the files off with an SDXC-capable reader first.
How to fix it
- Use a card of 32 GB or less (SDHC) in that device. Look for the SDHC or SDXC logo on both the host and the card.
- Use an SDXC-capable reader or device to access an SDXC card.
- Check the manufacturer for a firmware update; some devices gained SDXC support that way.
Some SDHC hosts will work with an SDXC card reformatted to FAT32, but that's outside the SD standard and isn't guaranteed to work.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.4 lists memory cards under removable storage, and the Core 1 acronym list includes SD, FAT32 and exFAT. When a scenario describes a large new card that an older camera or reader won't recognize, or that the device wants to format, think SDXC card in an SDHC-only host.