"The device is not ready" (error 0x80070015 or error 21) appears when Windows detects a drive but cannot read its contents. It is common on external USB drives, SD cards in card readers, optical drives, and occasionally internal drives.
Part 1. Common Causes by Device Type
| Device | Most Common Cause | First Fix to Try |
|---|---|---|
| SD card in reader | Empty reader or wrong card format | Reseat card, check file system |
| USB flash drive | Drive letter not assigned | Check Disk Management |
| External HDD | File system corruption or no power | CHKDSK or cable swap |
| Internal drive | Driver issue or drive failure | Device Manager reinstall |
| Optical drive | No disc inserted or dirty lens | Insert disc, clean lens |
⚠️ Important: If the error appears on a drive that previously worked, do not assume the drive is dead. Windows frequently shows this error when a drive letter is missing (visible in Disk Management), when a driver needs refreshing, or when the file system has a minor corruption.
Part 2. Check Disk Management for a Missing Drive Letter
- Press
Win + X→ Disk Management - Find the drive that shows "The device is not ready"
- If the drive appears but shows no drive letter, right-click → Change Drive Letter and Paths → Add
- Assign a letter → click OK
After assigning a letter, try accessing the drive again in File Explorer.
💡 Tip: In Disk Management, also check if the drive shows as "Not Initialized." Do not click Initialize — this wipes the partition table. Instead, run data recovery software first if the drive contains files.
Part 3. Reinstall the Drive Driver
- Open Device Manager (
Win + X→ Device Manager) - Expand Disk Drives or Universal Serial Bus controllers
- Right-click the affected device → Uninstall Device
- Disconnect and reconnect the drive
- Windows reinstalls the driver automatically
| Disk Management Status | What It Means | Next Step |
|---|---|---|
| Healthy — no letter | Drive readable but unadressed | Assign a drive letter |
| Not Initialized | Partition table missing/corrupted | Use data recovery before initializing |
| RAW | File system unreadable | Data recovery software (CHKDSK won't help) |
| Unknown | Drive not recognized | Try different port/cable; check Device Manager |
| Unallocated | No partition exists | Create partition (data will be gone) |
Part 4. Run CHKDSK If the Drive Is Accessible
If the drive has a letter but still shows the error when opening files:
chkdsk E: /f /r
💡 Tip: If the drive shows intermittently (appears then disappears) — this is not a file system error but a hardware issue. Check power delivery (use a powered hub for 3.5" drives), try a different cable, and test on a different PC before proceeding with software fixes.
🗣️ r/techsupport user: "Got device not ready on my SD card. Checked Disk Management and it was there but had no drive letter. Assigned one and it worked instantly. No data loss, no repair needed."
🗣️ r/datarecovery tip: "When 'device is not ready' appears and nothing else works, check if the drive appears in Device Manager at all. If it shows with a yellow exclamation mark, the driver is the issue — uninstall and let Windows reinstall it automatically on reconnect."
Part 5. Recover Files From the Inaccessible Drive With Ritridata
If the fixes above do not restore access and the drive contains files you need, Ritridata can scan the drive at the sector level and recover files — even from drives showing "the device is not ready" errors.
💡 Tip: Even if the drive shows "the device is not ready" in File Explorer, it may still appear in Ritridata's drive list — recovery software accesses drives at a lower level than File Explorer. Try selecting the drive in Ritridata even if it looks inaccessible in Windows.
Step 1 — Select the affected drive from the drive list (it may appear even if not accessible in File Explorer)
Step 2 — Run a safe scan — the drive is not modified during the process
Step 3 — Preview and recover files to a healthy drive
FAQ
What does "the device is not ready" mean? Windows can detect the hardware device but cannot access its contents. This is different from a drive not being detected at all — the device exists in Disk Management but the file system is either absent, unformatted, or experiencing access errors.
Can this error appear on a working drive? Yes — a working drive with a missing drive letter, recently plugged in that Windows hasn't fully initialized, or with a minor driver hiccup can show this error. Check Disk Management and try a driver reinstall before assuming drive failure.
Why does my SD card show device not ready? An empty card reader shows this error by design — there is no card to read. If a card is inserted and the error appears, try a different card reader, check that the card is properly seated, and verify the card is not write-protected (physical lock switch on the side).
Can data recovery software access a drive showing this error? In many cases yes — recovery software operates at a lower level than File Explorer and can often access drives that Windows refuses to open normally. If Disk Management shows the drive with the correct capacity, recovery software has a reasonable chance of scanning it.