When an SD card or USB stick doesn’t show up, the problem is usually one of three things: Finder is set to hide it, macOS sees the device but can’t mount it, or the Mac isn’t detecting it at all. Disk Utility tells you which. If the files on it matter, don’t click Initialize, format, or repair it until they’re safe. Those steps can make the files harder to get back.
Go through these in order. The first ones take seconds.
1. Check Finder’s settings
Finder can be set to hide external drives even when they’re working.
- In Finder, choose Finder ▸ Settings.
- Click General and select External disks to show them on the desktop.
- Click Sidebar and select External disks under Locations.
2. Check the connection
- Reinsert the card at a steady speed. Apple notes that inserting a card too slowly or too quickly can stop it mounting. Full-size cards go in with the metal contacts facing down and toward the Mac.
- Try another port, cable or reader. Plug in directly rather than through a hub or dock. A microSD card needs an SD adapter or a reader; try a different adapter if you have one.
- Restart the Mac with the card out, then insert it again.
- Try another computer. If no computer sees it, the card or stick itself is the problem.
3. Allow the accessory (Mac laptops)
On Mac laptops with Apple silicon, a new or unknown USB device or SD card may need your approval before it can connect. If you clicked Don’t Allow, or didn’t see the alert, the Mac ignores the device. Choose Apple menu ▸ System Settings ▸ Privacy & Security, click Accessories, and check the setting for Allow accessories to connect. Unlock the Mac, then reconnect the device.
4. Look in Disk Utility
Open Disk Utility (in Applications ▸ Utilities) and choose View ▸ Show All Devices. Now find your card or stick in the sidebar. What you see there tells you what’s wrong:
| In Disk Utility | What it means | What to do |
|---|---|---|
| The device and its volume, normal | It’s mounted. Finder is hiding it. | Go back to step 1. |
| The volume name is dimmed | The device is fine, but the volume isn’t mounted. | Select it and click Mount once. If that fails, see below. |
| Only the device, no volume | The file system is missing or damaged, or it’s a format the Mac can’t read. | Recover the files first (below). |
| Not listed at all | The Mac isn’t detecting the hardware. | Check the connection and accessory settings. If it’s still missing, see the last section. |
You can also check whether the Mac sees the hardware in Terminal with diskutil list, which only lists disks and changes nothing. A card or stick that appears there but not in Finder is detected but not mounted.
“The disk you attached was not readable by this computer”
This message offers Initialize, Ignore and Eject. Initialize leads to erasing the card. If you need what’s on it, click Ignore. The card often still has all its files, but its file system index is damaged, or it was formatted by a device in a format macOS doesn’t support.
5. Get the files off before you repair or format
The usual advice for a card that won’t mount is to run First Aid or to reformat it. Both write to the card. Formatting replaces its index, and repairs can change it, so do them only after your files are safe, or if the card holds nothing you need.
A recovery app reads the card directly, without macOS mounting it. Reco is free and opens the card read-only:
- Open Reco and choose the card or stick from its list. It’s listed there even when it isn’t mounted, as long as it appears in Disk Utility.
- Run a deep scan. You can pause, quit or unplug, and Reco continues where it stopped.
- Review the thumbnails and each file’s grade (Excellent, Good or Partial), then recover to a different drive.
Reco reads exFAT, FAT32, NTFS, APFS and Mac OS Extended drives. For step-by-step help, see SD card recovery on Mac or USB flash drive recovery.
Once your files are safe, you can run First Aid in Disk Utility, or erase the card and start fresh. For a camera card, format it in the camera you’ll use it in.
If it doesn’t show up anywhere
If the card or stick isn’t in Disk Utility and not in diskutil list, on any computer, with any reader, the Mac can’t talk to it. No software can read a device macOS can’t see, Reco included. A card that’s cracked or bent, or a USB stick with a loose or broken connector, needs a data recovery lab.
If the device keeps appearing and disappearing, that’s a sign it’s failing. Copy it once with Reco’s Copy first while it’s connected, then scan the copy instead of the device. To see what a drive reports about its own health, use Drive Check-up.
Questions
Why does my SD card show in Disk Utility but not in Finder?
Either Finder is set to hide external disks, or the card isn’t mounted. Turn on External disks in Finder ▸ Settings, then check Disk Utility: a dimmed name means the card is there but not mounted, often because its file system is damaged.
How do I fix an unreadable SD card on a Mac without losing data?
Recover the files first, then fix the card. Don’t click Initialize, and don’t format or run First Aid before your files are safe. A recovery app like Reco reads the card directly, so it can work on a card macOS won’t mount, as long as the card appears in Disk Utility.
Why doesn’t my MacBook see my SD card or USB stick at all?
On Mac laptops with Apple silicon, a new accessory has to be allowed before it can connect. Check System Settings ▸ Privacy & Security ▸ Accessories. Also try another port, cable or card reader, and plug in directly rather than through a hub.
Does a locked SD card stop it showing up?
A locked card should still appear, but macOS treats it as read-only, so you can’t change or delete anything on it. To write to it, eject it, slide the lock tab to the unlocked position, and insert it again.