fdchk - Floppy Disk Checker for Windows 9x ⎇

A surface scanner, FAT12 consistency checker, file-recovery utility, defragmenter and raw-FDC head diagnostic for Windows 9x (95/98/Me). Licensed under version 3 of the GNU GPL, and that version only (GPL-3.0-only) - the "any later version" option is not granted. See LICENSE. Report bugs to <k@iczelia.net>.

Test modes ⎇

1. Standard - read-only verification. Reads every sector and reports

anything that does not come back cleanly.

1. Thorough - destructive per-sector surface test: read the original,

then write-and-verify the original, its inverse, a PRNG block and that block's inverse, and finally restore the original.

1. Diagnostic - probes the drive with raw FDC commands through

fdchk.vxd, surfacing the full ST0/ST1/ST2/C/H/R/N result phase.

1. Check filesystem - walks FAT12 read-only for cross-linked clusters,

lost chains, size mismatches, chain cycles and bad FAT entries.

Other operations ⎇

• Recover - after a surface scan, walks the directory tree, copies out

every file with zero-filled holes where bad sectors fell, and writes fdchk-recovery.log. With auto-fix on, new bad clusters are marked 0xFF7 in both FATs.

• Format - FAT12 format at any capacity the drive supports. Quick

rewrites the boot sector, both FATs and the root directory. Full first re-lays every track through the driver's track formatter (Int 21h 440Dh CX=0842h, then CX=0862h to verify), which rewrites the sector ID address marks, data address marks and CRCs.

• Defrag - repacks files and subdirectories into contiguous low

clusters (depth-first, alphabetical at each level) and zeroes every free cluster.

• Batch mode - after each scan, prompts to insert the next disk.
• Logs - an in-app viewer for the log files in <exe-dir>\logs.

Diagnostic colours ⎇

In Diagnostic mode the grid becomes a cyl x head map, sized from the drive (160 cells for an 80-cylinder drive, 80 for a 40-cylinder one):

Build ⎇

Requires i686-w64-mingw32-gcc and nasm; mtools is needed only for make floppy.

make           fdchk.exe + fdchk.vxd
make floppy    fdchk.img - a 1.44 MB FAT12 image carrying the EXE
make debug     with-CRT build carrying symbols
make clean