dencorso

On Superfloppies and their Images

162 posts in this topic

The 640K floppies used 512 byte sectors, and were 80/2/8. They were just a 80 cylinder version (DSHD) of the original 320K format. And they used 2 sectors/cluster. I don't see any reason to remove support for this image format, as it's uncommon but "well behaved".

The 1232K (JPN) and 1280K (JPN) were really unusual formats, used by the NEC PC-98 family.

I've read that they can be read from DOS, when one has a 3-mode FDD. I have no info as to whether it was actually possible to boot DOS from them, but I think it unlikely. Furthermore, I have no objection to removing support for those two (really odd) image formats.

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The 640K floppies used 512 byte sectors, and were 80/2/8. They were just a 80 cylinder version (DSHD) of the original 320K format. And they used 2 sectors/cluster. I don't see any reason to remove support for this image format, as it's uncommon but "well behaved".

The 1232K (JPN) and 1280K (JPN) were really unusual formats, used by the NEC PC-98 family.

I've read that they can be read from DOS, when one has a 3-mode FDD. I have no info as to whether it was actually possible to boot DOS from them, but I think it unlikely. Furthermore, I have no objection to removing support for those two (really odd) image formats.

I would assume the 1280K is readable. The 1232K should also be readable if the track spacing is not modified. Assuming 512B Sectors, and readability, you should be able to boot from them.

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That's precisely the problem, RLoew: the track spacing is standard, however they don't use 512B sectors, but 1024B sectors instead.

1.25M (1232K)
-----------------------------
JPN Standard; Type: 5.25 Inch.
77 Tracks; 8 Sectors/Track;
1 Sector/Cluster; *1024 bytes/sector*;
224 Root directory entries;
1,232 Total sectors on disk;
1,249,280 Bytes available for files.

1.28M (1280K)
-----------------------------
JPN NonStandard; Type: 5.25 Inch.
80 Tracks; 8 Sectors/Track;
1 Sector/Cluster; *1024 bytes/sector*;
224 Root directory entries;
1,280 Total sectors on disk;
1,298,432 Bytes available for files.

jaclaz is implicitly referring to a list of supported floppy formats included in the floppy image creating spreadsheet he created (the latest version of which is some posts above). That list derives from various sources, including a list of floppy formats I compiled from many sources (and posted previously in the Floppy Emulation thread), from which I quoted the above excerpt.

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That's precisely the problem, RLoew: the track spacing is standard, however they don't use 512B sectors, but 1024B sectors instead.

1.25M (1232K)
-----------------------------
JPN Standard; Type: 5.25 Inch.
77 Tracks; 8 Sectors/Track;
1 Sector/Cluster; *1024 bytes/sector*;
224 Root directory entries;
1,232 Total sectors on disk;
1,249,280 Bytes available for files.

1.28M (1280K)
-----------------------------
JPN NonStandard; Type: 5.25 Inch.
80 Tracks; 8 Sectors/Track;
1 Sector/Cluster; *1024 bytes/sector*;
224 Root directory entries;
1,280 Total sectors on disk;
1,298,432 Bytes available for files.

jaclaz is implicitly referring to a list of supported floppy formats included in the floppy image creating spreadsheet he created (the latest version of which is some posts above). That list derives from various sources, including a list of floppy formats I compiled from many sources (and posted previously in the Floppy Emulation thread), from which I quoted the above excerpt.

A low level driver would be able to read and write 1K Sectors but I doubt that the BIOS would try Sector sizes other than 512B. None of my BIOSes would even handle the 4K Sectors of my USB 3TB Hard Drive.

This would make the Disks unbootable without an alternate Device based DDO.

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Yeah, that's what I think, too. That's why I agree those 1024B sector formats should be removed from the floppy image creating spreadsheet. While they may be of historical interest, they are useless for boot floppies.

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OK, I'll dump the 1232K and 1280K formats. :thumbup

More generally only 512 Bytes/Sectors will be included (besides the booting aspect, I suspect that non 512 bytes/sector formats would have anyway problems in VM's and/or Virtual Drives).

For the record there are the 8.00" floppy formats:

http://support.microsoft.com/kb/75131/en-us

that do have a different sector size, and they will be ignored also.

About the 640 Kb, it is OK as 80/2/8, and with 512 bytes/sector and with 112 Root Entries, I only wanted a confirmation that it has EITHER:

  1. Cluster size of 2 sectors and THEN a FAT of 2 sectors

    Floppy Formats Size Sectors C H S B/S S/C Re Mt Fatsize
    640K 655.360 1.280 80 2 8 512 2 112 251 2


    OR:

  2. Cluster size of 1 sector and THEN a FAT of 4 sectors

    Floppy Formats Size Sectors C H S B/S S/C Re Mt Fatsize
    640K 655.360 1.280 80 2 8 512 1 112 251 4


The issue is probably derived by a typo :ph34r: , as often happens when assembling together different sources with different data and trying to fill the gaps.

Another issue I am having is that in the list *appeared* (somehow) two different 320 K formats:

 
Floppy Formats Size Sectors C H S B/S S/C Re Mt Fatsize
320K (80/1/8) 327.680 640 80 1 8 512 1 ? 250 1
320K (40/2/8) 327.680 640 40 2 8 512 1 112 255 1

Are they BOTH valid?

If yes, how many root entries in the 80/1/8 version? 64 or 112? :unsure:

Additionally (and regarding both the 640K and the two 320 K):

Did they ever existed formatted in FAT12?

jaclaz

Edited by jaclaz
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The 640K size is the 8 sectors per track version of the common 720K size, from a time drives (or media) couldn't do 9 sectors per track reliably. It was the first format standard for the 3.5" floppies.

So, yes, 2 Sectors/Cluster and THEN a FAT of 2 sectors. It survived longer in Japan, but was used worldwide for a very short time.

The 320K size is the 2 sided version of the old 160K size, both also from a time drives (or media) couldn't do 9 sectors per track reliably.

So, yes, 2 heads and 40 tracks. It was the second format to be officially supported by PC-DOS, being introduced with v. 1.10. All later DOS versions support it natively up to V. 8.00, and I bet all Win NTs up to at least XP also do. And all DOS versions but 1.00 can boot from it.

So, yes, both the above existed in the wild as FAT-12 floppies, although the 640K never made it to the list of formats supported by DOS FORMAT. Of course, v. 7.xx and 8.00 should boot OK from a 640K floppy.

I think I once read a mention to a single-sided 80 track version of a 320K floppy in a post by Multibooter (yet I may be wrong), but that's the only reference I can think of for it, and it sure was never a common DOS floppy format. I'm positive this format can be dropped too. The sole single-sided formats that need support are 160K and 180K, because they are standard from very early on, which support was never dropped. I do still have a working MS-DOS 5.00 160K boot floppy I created just for fun more than 10 years ago. I've just booted from it and chkdsked it, to confirm it still works, while writing this. :P

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Very good. :thumbup

Still an issue :( : Media Type :ph34r: :

We have (for sure) the 3.5" "official" formats (as per given link on MS)

720K	1.44 MB	2.88 MB
F9 F0 F0
249 240 240

and the "official" 5.25" ones:

160K	180K	320K	360K	1.2 MB
FE FC FF FD F9
254 252 255 253 249

In the list *appeared" the 320K 80/1/8 with a Media Type of 250/FA. Is this possible? :w00t:

The 640K should be 251/FB. :unsure: Can anyone confirm this?

Maybe I found where I got some of the info:

http://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html

Media descriptor byte

The ancient media descriptor type codes are:

For 8" floppies:

fc, fd, fe - Various interesting formats

For 5.25" floppies:

Value DOS version Capacity sides tracks sectors/track

ff 1.1 320 KB 2 40 8

fe 1.0 160 KB 1 40 8

fd 2.0 360 KB 2 40 9

fc 2.0 180 KB 1 40 9

fb 640 KB 2 80 8

fa 320 KB 1 80 8

f9 3.0 1200 KB 2 80 15

For 3.5" floppies:

Value DOS version Capacity sides tracks sectors/track

fb 640 KB 2 80 8

fa 320 KB 1 80 8

f9 3.2 720 KB 2 80 9

f0 3.3 1440 KB 2 80 18

f0 2880 KB 2 80 36

For RAMdisks:

fa

For hard disks:

Value DOS version

f8 2.0

This code is also found in the first byte of the FAT.

IBM defined the media descriptor byte as 11111red, where r is removable, e is eight sectors/track, d is double sided.

OT, but not that much ;), this may open some new "formats" (which I didn't even suspect existed :blushing: ):

http://msdn.microsoft.com/en-us/library/windows/desktop/aa365231(v=vs.85).aspx

jaclaz

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Well, I guess you've got the Media Type Byte figured all right.

And since fa 320 KB 1 80 8 is bona-fide, I guess it should be include, despite being super-obscure.

But I still think support for non-512B sectored formats is unneeded, even if they are documented enough.

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Well, I guess you've got the Media Type Byte figured all right.

And since fa 320 KB 1 80 8 is bona-fide, I guess it should be include, despite being super-obscure.

But I still think support for non-512B sectored formats is unneeded, even if they are documented enough.

I have a working 1KB Sector Floppy Disk with only a few additional mods needed.

As I expected the BIOS will not boot the Disk, but a slightly non-standard format may make it possible to boot, if I can solve an internal Disk Geometry problem.

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Wow! Does it require a DDO, or just modding the bootstrap loader and IO.SYS can get it to boot?

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I had not quite grasped it was a single sided format (silly me!), but the 0xFA format is also in Thom Hogan's handbook, which relevant table I reproduced here. I think no format can be more officially recognized by MS than one which has its own Media Type Byte, so for me that's more than settled.

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Wow! Does it require a DDO, or just modding the bootstrap loader and IO.SYS can get it to boot?

To read or Write a 1K Sector Disk only requires a TBPLUS IO.SYS with one small Mod and a tiny Startup Program.

I have not yet succeeded in booting yet. A DDO probably will be required as the BIOS reports incorrect Geometry, and the BIOS is not correctly handling DMA wrap.

A 512B Bootstrap Sector is needed to switch the Disk Controller as the BIOS will not read 1K Sectors during Boot. I made a custom Format by adding one 512B Sector to the nine 1K Sectors on Track 0 Head 0. This creates 2 separate #1 Sectors, one 512B and one 1K. The DDO will go into the Bootstrap Sector.

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I have succeeded in booting the 1K Floppy with a 512B Bootstrap Sector without a DDO using a heavily modified IO.SYS. A DDO should allow using an unmodified TBPLUS IO.SYS.

Using 4K Sectors, it may be possible to Format 1.92MB.

Edited by rloew
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Not-necessarily OT...

...The MS standard (fatgen.pdf v. 1.03) has BPB_TotSec16 for BPB+0x10 and BPB_TotSec32 for BPB+0x1D...
I've beat my brains out over the Dell Utility/Recovery partitions MBR/PBR (using goodell's info). A worthy note is a "Sector 18" copy of some of the MBR (the Partition Table). Amazingly, the sectors AFTER the first Sector of the Partition (those "reserved" -NOT HIDDEN- sectors) is NOT 32, but rather 38!!!

If you search on "fatgen102" as opposed to using the kind-of CURRENT "fatgen103" the information, albeit a slight older, kind of helped me figure it out. They have many a warning about "false assumptions" (e.g. "how to REALLY identify fat12-fat16/fat32). Of course, you all may already know this...

edit - durr!!!

BTW, interest in this is because I have two Iomega Zip-100 (IDE-cable type) and a single (apparently foobared by a shop magnet) disk and it would be interesting in "resurrecting" it since the dang things are hard to find and rather expensive. :(

Thread subscribed...

Edited by submix8c
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