Why can't I format to 720k \ VOGONS

Why can't I format to 720k

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First post, by jarreboum

Posted on 2017-09-01, 12:21

jarreboum Offline

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[edit] This solved itself neatly when using new floppies. Don't be an idiot, don't use old floppies to do your testing!

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I'm a bit confused. I'm trying to format a DSHD floppy to 720k by booting the PC with a DOS 6.22 boot disk, but all I get is an error message.

> FORMAT /F:720 A: Insert new diskette for drive A: and press ENTER when ready... […]
Show full quote
> FORMAT /F:720 A:
Insert new diskette for drive A:
and press ENTER when ready...

Formatting 720K
Invalid media or Track 0 bad - disk unusable.
Format terminated.
Format another (Y/N)?n

General failure reading drive A
Abort, Retry, Fail?

A perfectly good DSHD floppy is rendered unusable. Note that I can still format it to 1.44 afterwards without any issue. As an aside, DOS doesn't give a damn about the HD hole in the floppy. It will format to 1.44M by default regardless of the type of disk I insert. Covering the hole of a DSHD disk with tape still make it format to 1.44M with the default FORMAT A: command.

I remember formatting floppies to 720K, but that was on another PC and another drive. I'm on a fairly recent Athlon64 machine, and the drive is an old Epson SD800.

Also note that I can still use the floppies as double density on other computers: I have an Amstrad CPC6128 modified to use DSDD 3.5 floppies, and it can format them to its own file system without a problem.

Last edited by jarreboum on 2017-09-01, 13:54. Edited 2 times in total.

Reply 1 of 7, by Deksor

Posted on 2017-09-01, 12:27

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Your floppy drive probably don't have the 720K sensor.

Change it with another one and you should be fine

Trying to identify old hardware ? Visit The retro web - Project's thread The Retro Web project - a stason.org/TH99 alternative

Reply 2 of 7, by jarreboum

Posted on 2017-09-01, 13:29

jarreboum Offline

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welp, nevermind, I'm an idiot.

Don't use old floppies when testing stuff, kids!

Reply 3 of 7, by Errius

Posted on 2017-09-01, 13:50

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Dust inside the drive blocking something? Shoot some compressed air in there. You need to avoid knocking the head out of alignment though. That's not fixable.

Is this too much voodoo?

Reply 4 of 7, by 640K!enough

Posted on 2017-09-01, 17:22

640K!enough Offline

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EDIT: Maybe add the /u switch to the /f:720 you already have? It tries to do a "safe format" by default as of MS-DOS 5.0. Also, my systems insist on having the format detection hole blocked. Unless they can't reliably hold data in any format, old floppies should generally work about as well as new for these purposes.

Reply 5 of 7, by jarreboum

Posted on 2017-09-01, 19:26

jarreboum Offline

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640K!enough wrote:
EDIT: Maybe add the /u switch to the /f:720 you already have? It tries to do a "safe format" by default as of MS-DOS 5.0. Also, my systems insist on having the format detection hole blocked. Unless they can't reliably hold data in any format, old floppies should generally work about as well as new for these purposes.

I thought I tried that, but maybe I didn't. Using /U worked, but one disk grinded a lot in the last few %, and I ended with 47,104 bytes in bad sectors. This one is going in the trash. The other one was fine, and I was able to format it again without /U.

This lack of detection of the disk density is troubling though. Does FORMAT A: do a 720K format on a DD disk in your drive, guys? Just to make sure before I take it apart 🤣

Reply 6 of 7, by Deksor

Posted on 2017-09-01, 22:08

Deksor Offline

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Without the /F:720 switch, none of my fdd do format 720k floppies into 720KB just like none of my 1.2MB 5"1/4 FDD will format a 360KB floppy disk into 360KB unless I use the /F:360 switch

Trying to identify old hardware ? Visit The retro web - Project's thread The Retro Web project - a stason.org/TH99 alternative

Reply 7 of 7, by 640K!enough

Posted on 2017-09-02, 04:27

640K!enough Offline

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The behaviour of my systems is the same as Deksor posted (/f: switch required for lower capacities), but I will also add that my system refuses to complete a format of a high-density diskette as a double-density diskette if the hole is not blocked (I just tried to be sure); it will fail after trying, rather than checking and giving an intelligent error message.

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