Notes on cleaning and testing floppy disks and drives

modified: 31 Mar 2005

I've seen a number of posts in which people have related problems with installing Minix from floppy disks.

One cause of such problems may be old and unused floppy disk drives. As anyone who has ever tried to do a thorough job of cleaning an old PC has probably noticed, the floppy drive is an important path by which airborne dust is sucked into a computer. If you take the cover off a floppy drive from an old computer you will often find a lot of dirt in there.

Floppy disks are no longer the means by which most new programs are installed -- CD-ROMs have much higher capacity and are cheaper to produce. And now that most computers have network connections, writeable CD-ROM drives, and other means of storing data on high capacity media, floppy drives may not get exercised frequently, and this can contribute to the problem. Occasional use will knock dust loose and wipe it away from the read/write heads. A drive that has not been used for a long time is likely to give errors unless it is cleaned.

Floppy drive cleaning kits that consist of a cloth disk that can be wetted with a cleaning fluid are well worth the cost. Using one of these kits on a floppy disk drive that has not been used much recently is often helpful. This can also save your disks -- dirt that causes errors in reading and writing can also scratch the coating on a disk, resulting in permanent errors.

In another article on my website I've noted the importance of using perfectly good disks when using the Minix vol(1) command or the MS-DOS/Windows rawrite and fdvol utilities or other tools which read and write raw data from and to a floppy disk without using any of the operating system data structures that can help to avoid bad sectors on the disk.

The Minix readall(1) and format(1) utilities are useful for diagnosing problems. If readall finds errors on a disk in different places on successive attempts, the errors are probably due to loose dirt, and use of the disk drive cleaning kit may cure the problem. If successive tests with readall show the same errors, then the disk is probably scratched or otherwise damaged. It seems to me that the Minix format program (with the -v option) is more sensitive than readall, and a disk that passes a readall test will sometimes show errors when you try to format it. When formatting, also, it is worth trying twice to see if the same errors appear.

I've noticed a hierarchy of usefulness of various tools in diagnosing whether a floppy disk is good. I have found the least reliable tool is the Windows disk error-checking tool. The Windows format program often reveals bad sectors that the error-checking program doesn't find. And the Minix tools sometimes reveal problems with a disk that passes the Windows tests.

BIOS settings and floppy drives

After I posted an article more-or-less identical to the above on comp.os.minix, Giovanni Falzoni added these comments:

Many recent BIOSes have an option to disable floppy testing at boot.

Do NOT enable this option. You get a faster boot but more dust is accumulated on the gears that move the heads. This may result in the heads getting stuck. The cleaning kit can't do any good in this case. You will need to disassemble the drive to get it cleaned.

I hadn't thought of this before, but it seems like a good point.