Sector Not Found
Microsoft MS-DOS PC
Severity: ModerateWhat Does This Error Mean?
Sector Not Found means DOS read the disk but could not find the expected sector. The disk has a physical or logical fault. This usually appears as part of the classic Abort, Retry, Fail? prompt.
Affected Models
- IBM PC
- IBM XT
- IBM AT
- Compaq Deskpro
- Any MS-DOS PC
- DOSBox emulator
Common Causes
- Floppy disk physically damaged (bad sector)
- Disk formatted at wrong density for the drive
- Dirty read/write head on the floppy drive
- Disk demagnetised from magnetic interference
- Hard disk bad sectors (serious)
How to Fix It
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Press R (Retry) once or twice first.
Sometimes a marginally readable sector succeeds on a second attempt. If Retry works, copy all data off the disk immediately — it is failing.
-
Clean the floppy drive head.
Use a floppy drive cleaning kit (a cleaning disk with fluid). A dirty head causes read errors even on perfectly good disks.
-
Try a different drive if available.
A disk that fails in one drive may read in another. Different drives have slightly different head alignments.
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Run CHKDSK on the disk.
Type CHKDSK A: (or the relevant drive letter) at the DOS prompt. CHKDSK reports bad sectors and attempts to mark them as unusable so DOS avoids them.
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For hard disk Sector Not Found: back up immediately.
A hard disk reporting Sector Not Found is a serious warning. Back up everything you can before attempting repair. SCANDISK (DOS 6.2+) or a third-party tool can attempt to remap bad sectors.
Frequently Asked Questions
Can I recover files from a disk with Sector Not Found errors?
Often yes — especially if only a few sectors are bad. Tools like Norton Disk Doctor (for DOS era) or modern tools like Recuva or TestDisk can sometimes recover files by reading around bad sectors. The sooner you try, the better.