Donald Duck wrote on Today, 19:10:

So you are saying that when he was refering to 2 X heads he ment both sides of the disk

Yes, I believe so - each of the two head read/writes one of the two sides of the disk.

DaveDDS wrote on Today, 19:17:

Donald Duck wrote on Today, 19:03:

... But this is single sided, 720mb right?

The PC never used single-sided disks. The main difference is DD (Double Density) .vs. HD (High Density)

The original XT had 5.25" DD drives - 40x2x9x512 = 360k

But where is the X2 comming from? because it was single sided right?

Donald Duck wrote on Today, 20:02:

DaveDDS wrote on Today, 19:17:

The original XT had 5.25" DD drives - 40x2x9x512 = 360k

But where is the X2 comming from? because it was single sided right?

I don't believe the PC ever officially used single-sided drives - the x2 is two heads (40 tracks, 2 heads, 9 sectors/track, 512 bytes/sector)

I think the XT might have used 8 sectors/track at first = 320k

The original XTs did use full-height drives - twice as tall as "modern" drives - this was also the form-factor of the first drive (SA-400) which was single-sided - perhaps this is confusing to some.
But double-sided full-height drives did exist (and were used in the XT) and there were even a few half-height single-sided drives along the way (which I never saw in a PC, but were used on some other systems)

To see what various drives physically look like, check out this pic:

http://dunfield.classiccmp.org/misc/h/floppy.jpg

Thas has:
8" full height
8" half height
5.25" full height
5.25" half height
3.5" desktop
3.5" laptop

DaveDDS wrote on Today, 21:22:

Donald Duck wrote on Today, 20:02:

DaveDDS wrote on Today, 19:17:

The original XT had 5.25" DD drives - 40x2x9x512 = 360k

But where is the X2 comming from? because it was single sided right?

I don't believe the PC ever officially used single-sided drives - the x2 is two heads (40 tracks, 2 heads, 9 sectors/track, 512 bytes/sector)

DaveDDS wrote on Yesterday, 02:08:

> FORMAT A: /T:80 /N:9

Donald Duck wrote on 2026-09-26, 19:00:

I have a batch of 3.5" Atari disk (DS and DD).

So the 3.5” disks that I formatted are double sided and double density And are of 9 sectors each on 80 tracks on each side (512 bytes x9x80x2=737.280 MB)

So if I want to format a 3.5” double sided and double density which is 1.44mb which is double the original? is it double the the amount of sectors per track or double the total of tracks?

This may help:
https://forum.vcfed.org/index.php?threads/a-q … py-disks.26266/

EduBat wrote on 24 minutes ago:

This may help:
https://forum.vcfed.org/index.php?threads/a-q … py-disks.26266/

That link states the following

Double Sided/Double Density (DS/DD): 80 track, 9 sectors per track, 512byte sectors. 720k.
135TPI, 665 oersted media. 250Kb/sec data rate. 300RPM

Double Sided/High Density (DS/HD): 80 track, 18 sectors per track, 512byte sectors. 1.4mb.
135TPI, 720 oersted media. 500Kb/sec data rate. 300RPM

Again, we have a higher data rate for high density. But the number of tracks is the same! This means that a high density 3 1/2" drive can write DD disks exactly as well as a DD drive can. No more incompatibility problems between drives.

DaveDDS wrote on Yesterday, 02:08:

> FORMAT A: /T:80 /N:9

So if I am going to format a DS HD 1.44mb 3.5" floppy
Is this the correct command?

> FORMAT A: /T:80 /N:18

Donald Duck wrote on Today, 22:02:

So the 3.5” disks that I formatted are double sided and double density And are of 9 sectors each on 80 tracks on each side (512 bytes x9x80x2=737.280 MB)

Yes.

So if I want to format a 3.5” double sided and double density which is 1.44mb which is double the original? is it double the the amount of sectors per track or double the total of tracks?

For a PC It's 18 sectors/track instead of 9 - still 80 tracks (all 3.5" diskettes are 80 track)

Just make sure you have the right media - as I described in an earlier post, HD dislettes are different media and have an "extra" hole near the top of the left side (DD diskettes do not have a this hole) which the drive/system uses to identify it as HD.

IIRC Winblows 7+ always defaults to HD, so you should be able to format it from the GUI or from the command line without any extra arguments to FORMAT.

Lots of detail here: http://www.csgnetwork.com/fdi.html

The original 1981 IBM PC used single-sided disks that formatted to 160 KiB under DOS 1.0.