Last revision of this page: February 8, 2025

Please refer to the manual of your hard disk controller to see if it actually can low level format (LLF) a hard disk with DEBUG. If yes, basically follow these steps:

1. Boot into DOS
2. Run DEBUG
3. At the DEBUG prompt (-) enter:

MANUFACTURER	ROM START ADDRESS
Wester Digital	C800:5
DTC	C800:5
Adaptec	C800:CCC
Seagate	C800:5
SMS-OMTI	C800:6
Alternate address	CA00:5
Alternate address	CE00:5
WD-1007V-SE1, WD-1007V-SE2	CC00:5
WD-1003V-SR, WD-1006V-SR / Rev F003, F005	CC00:5

With some manufacturers it is possible or necessary that you first select the drive in DEBUG and then set the interleave factor. Western Digital requires that you set the drive in AH and the interleave in AL:

AH = 00 → C: or AH = 01 → D: and AL = 04 → Interleave 4

This way of LLF is mainly encountered with the first 8 bit MFM hard disk controllers. The later 16 bit controllers could be tested and configured very comfortably with special programs like SPEEDSTOR, SPINRITE, ONTRACK DISK MANAGER. I use the programs SPEEDSTOR and SPINRITE for my MFM hard disks.

A further disadvantage of the old 8-bit controllers is that the hard disk and the controller are exactly matched to each other. A hard disk formatted with controller A cannot be used with controller B from another company.

IBM Fixed Disk Adapter (IBM/Xebec)

The DEBUG method does not work with the original IBM/Xebec controllers. The jump to the address C800:5 leads here into the void. For more information see Minuszerodegrees: IBM Fixed Disk Adapter - Low-Level Format via DEBUG.

With these Xebec controllers I always use SpeedStor version 6.0.3 and afterwards I check the hard disk with Spinrite II. With Spinrite the interleave can be adjusted optimally.

For the combination 62X0786 (Var #3) and ST225 I use the Interleave of 5. I have checked this with Spinrite II => 5.

IBM Fixed Disk and Diskette Drive Adapter (IBM/Western Digital)

The DEBUG method does not work with the original IBM/Western Digital controllers. The jump to the address C800:5 leads here into the void. For more information see Minuszerodegrees: IBM 5170 - Low-Level Format for Supplied Controller.

In the 286 BIOS of AMI there is certainly a wonderful function: ROM DIAGNOSTICS. Right at the beginning in the HARD DISK menu you can test and format your hard disk in detail: Media surface analysis, interleave determination and low-level formatting. The advantage is that you do not have to boot your computer into DOS at all.

Western Digital (WD1002S-WX2A, PCB Rev. "X1")

Western Digital (WD1002S-WX2A, PCB Rev. "X12")

CTT Munich (IT-805)

The CTT Munich (IT-805) controller already has a relatively comfortable interface. Even defective cylinders can be entered here at the end of formatting.

MANUFACTURER	ROM START ADDRESS
Adaptec AHA-154X	-G=DC00:6 (Onboard utilities incl. LLF)
Adaptec AHA-154X	-G=DC00:9 (DMA channel test)

• Microsoft Knowledge Base Articles: Q60089 Using DEBUG to Start a Low-Level Format

• minuszerodegrees: IBM Fixed Disk Adapter - Low-Level Format via DEBUG
• minuszerodegrees: IBM 5170 - Low-Level Format for Supplied Controller