ARCHIVED: How do I low-level format an MFM or RLL drive?

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A low-level format actually does a physical format; it lays down tracks and sectors. It is the first format for a hard disk, and is used later to extend the life of an old drive to refresh the media. It wipes all information, just like reformatting a floppy disk.

Doing a regular format on a hard drive merely re-organizes the File Allocation Table (FAT), and doesn't really erase the disk or lay down tracks and sectors.

Spinrite, mentioned below, actually reads information off the disk, and re-writes it as it finishes formatting sectors on the disk, which is why it is not destructive like an ordinary low-level format. The instructions below work for small-disk Western Digital and Adaptec MFM and RLL controllers. Newer controllers usually use bundled software for low-level formatting.


It is best to do this from a bootable floppy. The floppy should have DEBUG.COM, FDISK.COM and FORMAT.COM on it.

The old 10MB IBM XT drives have to be low-level formatted using a routine on the IBM Advanced Diagnostics diskette. Zenith machines use the PREP command in Zenith DOS. Other older machines require use of the debug utility.

At the A:\> prompt, type:


You will get a "-" prompt. At this point, type:

  G=C800:5  -or-      for Western Digital controllers
  G=C800:CCC          for Adaptec controllers.
  G=C800:5            for DTC (Data Technonolgy) controllers

  G=C800:6            for OMTI controllers

Spinrite is a good alternative to ordinary low-level formatting, because it doesn't destroy the contents of a disk. However, it does not work with many kinds of drives, especially those that use sector translation.

This is document aaoa in the Knowledge Base.
Last modified on 2023-09-22 17:25:12.