How to Scan Bad Sectors in MS-DOS 6.22

In MS-DOS 6.22, the primary system utility used to scan hard drives for bad physical sectors is ScanDisk. Introduced in MS-DOS 6.0 and significantly refined in version 6.22, ScanDisk replaced the older CHKDSK utility for deep diagnostic tasks. While CHKDSK primarily resolved logical file system errors, ScanDisk incorporates a dedicated surface scan routine capable of testing magnetic media for physical defects, relocating readable data, and flagging defective sectors to prevent future data loss.

The Role of ScanDisk

ScanDisk (SCANDISK.EXE) is an interactive diagnostic program designed to check both the logical structure of a disk and the physical integrity of the storage media. When operating on a drive, it examines the File Allocation Table (FAT), directory structures, file system integrity, and physical clusters.

Unlike previous DOS diagnostic commands, ScanDisk includes a dedicated "Surface Scan" test. During this test, the utility systematically reads every sector on the disk to determine if the read heads encounter errors or unreadable blocks. If a sector is unreadable, ScanDisk attempts to recover any existing data from the damaged area, moves that data to a healthy cluster, and marks the damaged cluster as "bad" in the FAT. Once marked, MS-DOS will no longer attempt to read from or write to that physical location.

Running a Surface Scan

To initiate a scan on a hard drive using the interactive text-based interface, enter the following command at the DOS prompt:

SCANDISK C:

Once the initial file structure checks are complete, ScanDisk automatically prompts you to perform a surface scan. Selecting Yes begins the physical read test across the entire drive partition.

To bypass the prompt and execute an immediate, non-interactive, or automated physical scan, specific command-line switches can be used:

  • Direct Surface Scan:
    SCANDISK C: /SURFACE
    Forces ScanDisk to immediately perform a surface scan right after completing file structure checks without prompting.

  • Unattended Scan with Auto-Repair:
    SCANDISK C: /AUTOFIX /SURFACE
    Instructs ScanDisk to fix any logical errors and bad sectors automatically without requiring user intervention.

  • Non-Interactive Batch Mode:
    SCANDISK C: /AUTOFIX /NOSAVE /SURFACE
    Repairs errors, performs the surface scan, and deletes lost cluster chains rather than saving them as files, which is ideal for automated maintenance routines.

ScanDisk remains the standard and most reliable built-in tool for physical sector verification and drive maintenance across the MS-DOS 6.x operating system family.