Sector‑by‑Sector Backup of Floppy Disks with MS‑DOS DISKCOPY

Goal

The objective is to create an exact sector‑level clone of a floppy disk so that the backup can be restored to any compatible DOS system. DISKCOPY copies every sector, including boot sectors, hidden data, and bad‑sector information, making it ideal for forensic or archival purposes.

Prerequisites

• MS‑DOS 6.x or later (earlier versions may lack full support for 1.44 MB disks).
• Two writable floppy drives (e.g., A: and B:). The target drive must be empty or contain a backup disk; data will be overwritten without warning.
• Write protection disabled on the source disk.
• Standard 1.44 MB, 720 KB, or 1.2 MB disks. Non‑standard formats (e.g., 2.88 MB) are not guaranteed to work.
• Optional: a third‑party disk‑image driver if you need to copy to a file instead of a physical disk.

Procedure

1. Insert the source disk into drive A: and the target disk into drive B:.

   DISKCOPY A: B:

2. Press Enter to start. DISKCOPY displays a progress bar and writes sectors directly to B:.
   • It does not prompt for confirmation; ensure B: is ready before executing.
   • If the command fails, it will abort and leave B: in a partially written state.
3. When the process completes, DOS shows one of the following status codes:
   • 0 – Success.
   • 1 – Disk write error (often a bad sector on B:).
   • 2 – Source disk read error.
   • 3 – Disk copy aborted by user.

Verifying the Copy

DISKCOPY does not verify the data it writes. Use the built‑in file compare utility FC /B to perform a byte‑by‑byte check of the two disks. The command must be run from the command prompt with sufficient privileges (standard user is enough on DOS).

FC /B A: B:

If the output shows 0 differences, the disks are identical at the sector level. Any difference indicates a corrupted copy.

Additionally, confirm the size of the target disk matches the source:

DIR B:

The DIR output should show 1,474,560 bytes for a 1.44 MB disk.

Common Issues & Recovery

• Write Protection Enabled – DISKCOPY will fail with a write error. Disable protection or use a protected‑disk driver.
• Non‑standard Disk Format – DISKCOPY may abort. Use a disk imaging tool that supports the specific format.
• Partial Copy – If the copy aborts, re‑format the target disk before retrying. Use FORMAT B: to clear it.
• USB Floppy Adapter – Some adapters require DOS drivers (e.g., USBFLOP.SYS). Load the driver before running DISKCOPY.
• Large Disks (2.88 MB) – Some DOS versions cannot handle these. Verify with DISKCOPY A: B: and check the error code; if unsupported, use an alternative imaging tool.

Notes & Limitations

• DISKCOPY writes directly to the target drive; no confirmation prompts mean accidental overwrites are possible. Always double‑check the drive letters.
• The command cannot copy to a file. To create a disk image file, use a third‑party utility such as IMGDISK or install a disk‑image driver that presents the image as a virtual drive.
• DISKCOPY does not handle disk encryption or compression; it copies raw sectors.
• Verification is essential because the command does not report sector‑level integrity.

By following this guide, you can reliably clone floppy disks at the sector level, verify the integrity of your backup, and recover from common failure scenarios.