Low Format A Harddrive
| Field | General Computer Use |
| Went Obsolete | late 1990s |
| Made Obsolete By | Smart sector-remapping and servo tracks. SpinRite? |
| Knowledge Assumed | Minimal |
| When useful | When using a very old computer / repairing MFM, RLL or ESDI hard drives |
run the DEBUG.COM tool that came with DOS. At the DEBUG prompt (:) enter the command g=c800:5
This will execute the low level hard drive format tool that is built into the hard drive controller. Different hard drive controllers gave different options, including the ability to do a bad sector scan, or change the interleaving of the drive. Most early “White box” 1990s vintage computers had an option to low level format a hard drive in BIOS.
Low level formatting a “Winchester” MFM or RLL hard drive was necessary because these drives were “stupid” and didn't contain any servo tracks on the disk itself. The disk controller was primarily responsible for ensureing that the heads were in the right place.
Older “Squeaky” MFM and RLL drives used a servo motor which was then connected to a pillar which was then connected to a steel band, which moved the heads back and forth. The problem was, over time, the tracks would go out of alignment due to stretching of the steel band or misalignment of the stepper motor. As well, the aluminum platters of the drive would expand and contract over time, compounding the problem. Some users have mentioned that their MFM or RLL drives were unusuable until they “Warmed up”.
Thereby, it was necessary to periodically low level format the drive due to this misalignment. Unfortuantely, this would also destroy all of the data on the drive, requiring a standard OS reformatting.
Note: Low Level formatting will destroy late 1980s to mid 1990s IDE drives. Modern IDE drives will simply ignore low level formatting requests, however it's still not recommended as it's not necessary.
The need to low level format hard drives was made obsolete when modern IDE hard drives were smart enough to record servo information tracks on the disk itself, allowing the built-in controller on the drive to automatically reposition the heads for the most optimal read. These servo tracks tell the controller which track the heads are on and which position the disk is in. These tracks can also control the rotational speed of the disk as well.
Gibson Research (Steve Gibson) created a tool called SpinRite? which allowed users to non-destructively change the drive interleaving. As hard drives became faster and faster, interleaving was no longer necessary.
