DOS feature on formatting disk

From: jim stephens <>
Date: Tue Jan 18 17:25:25 2005

for media portability the track 0 was the directory on some
IBM formats, and probably the dos program is trying to bridge
the problem by forcing the whole track to have readable sectors
on it, so some other non dos programs won't blow.

I had experience doing a 8" driver at one time and was surprised
to find that the standard format for ibm was to have at least the first
sector present, but the rest could be "deleted" sectors, the lot of
could be replaced with other data sectors, and a string of deleted
ones again to add data.

Also track 0 frequently tells software that the format is for the entire

disk, and may have been assumed to be in a standard density, with
tracks 1 thru n in a different density, determined from track 0.

I think on 5 1/4" diskette formats IBM did look at a byte in the
first sector to tell 320 vs 360 or 160 vs. 180 k format. Later
bios' assumed a 360k format if the byte was not FF or FE, IIRC.

Some non dos os's were smart when designing their disk formats
to be used inthe IBM pc and kept the media byte, and some,
(like Pick for the PC) were dumb and had diskettes which looked
totally unformatted to the bios and to DOS when set up for
their use.


"Dwight K. Elvey" wrote:

> Hi
> DOS has an irritating feature when asked to format
> a disk. If track 0 is partially readable it will
> fail to format, even if you use the /u option.
> I've been moving data from one machine to another
> and the source machine has a flaky drive. It sometimes
> trashes track 0.
> I've found that the only way to get around this problem
> is to wipe the disk with a strong magnet.
> Why can't it just try to format first and then check
> track 0. Why must it fail to format because track 0
> is partially readable when I specifically asked it
> to unconditionally format?
> Dwight
Received on Tue Jan 18 2005 - 17:25:25 GMT

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