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 Post Posted: Sun Jun 18, 2017 12:59 am | Post subject: 5.25 disk images?
 
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Recently tried to write Windows 3.1 Disk 1 to a 5.25 floppy disk via my Windows 98 machine's newly installed 5.25 drive, and it failed in two different programs, one of them being DiskWrite and the other being a DOS program i cannot remember the name of at the moment.

Noticed that these images are 1,200kb (exactly 1.2mb) and my 5.25 floppies, when empty read 1.15mb free, so clearly it's failing because there is 50k of missing space. What's up with my 5.25 drive, is it a jumper in a wrong spot or something? My 5.25 disks are new old stock Verbatim disks which I can read and write to no problem but I do not have any other 5.25 disks besides these to test. I still have the box and it says IBM format and 1.6mb unformatted capacity and 1.2mb formatted, so it seems like they are correct...

Got any clues? I have the installation guide to my exact drive (the Mitsubishi MF504C) http://www.minuszerodegrees.net/manuals ... 0Guide.pdf

See any jumpers there that could be affecting it? I want to see if there is a software problem first before tearing the computer apart again, though. It is set in the bios properly as B: 5.25 1.2mb... Stumped.


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 Post Posted: Sun Jun 18, 2017 7:27 am | Post subject: Re: 5.25 disk images?
 
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This question is related with H/W.
You recommend to write it on H/W. thread next time if you want to ask H/W related question.

I use DCOPY.EXE to write to 5.25" drive from 5.25" disk image on real DOS.
(But you need formatted blank disk without bad sector.)

Example :
DCOPY FILENAME.IMG A:

I don't use Winimage for Windows.


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 Post Posted: Sun Jun 18, 2017 7:39 am | Post subject: Re: 5.25 disk images?
 
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The "1.6mb" number is marketing bullshit. Just ignore that number. The formatted capacity of a high density IBM PC 5.25" disk is 1.2mb.

A freshly formatted 1.2mb disk should report 1,213,952 bytes free in DOS. Otherwise it has bad sectors and can not be used for writing disk images. Writing whole disk images, as found here on Winworld, requires error-free disks.

For standard 1.2mb disks, you will probably have the best luck and fewer headaches writing with WinImage from inside Windows 9x.

Under DOS, I prefer to use ImageDisk, but "IMG" files must be converted to its format. The commands to convert to ImageDisk format are here: viewtopic.php?t=6931

But there are many, many, other disk writers for DOS. I don't have a good list of them. So you might find some other that works better for you.

If all of these disk are formatting with bad sectors, but are not physically damaged, it may be that the disk surface has accumulated a thin layer of residue. Seems to be a common problem. I'd suggest cleaning your drive heads, and try re-formatting the disks multiple times (can take a dozen or so tries). As odd as it may seem, high quality disk exhibiting that problems may actually become MORE readable after they have been use for a while.


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 Post Posted: Sun Jun 18, 2017 11:52 am | Post subject: Re: 5.25 disk images?
 
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Culbrelai wrote:
Noticed that these images are 1,200kb (exactly 1.2mb) and my 5.25 floppies, when empty read 1.15mb free, so clearly it's failing because there is 50k of missing space. What's up with my 5.25 drive, is it a jumper in a wrong spot or something?

Everything is correct.
Any normal 1.2Mb 5.25" floppy formatted to it's standard capacity contains 2 sides, 80 tracks / side, 15 sectors / track, each sector contains 512 bytes. So you can easily count the total disk space:
2 * 80 * 15 * 512 = 1.228.800 bytes

Formatted disk contains few required service structures: boot sector (512 bytes), 2 FAT12 copies (each is 3584 bytes) and directory table (contains 224 entries, each entry is 16 bytes). The total size of this service area is:
512 + 2 * 3584 + 224 * 16 * 2 = 14.848 bytes

So the total free space available for data is 1.228.800 - 14.848 = 1.213.952 bytes

And don't forget that traditionally storage capacity is not measured in kilobytes (kB), megabytes (MB) etc. but in kibibytes (KiB), mibibytes (MiB) instead. And when one kilobyte = 1024 bytes, 1 kibibyte = 1000 bytes. But programs still count free space in kilobytes and megabytes. And since 1 Mb = 1024 kB, 1 kB = 1024 bytes, you'll get:

1.213.952 / 1.024 / 1.024 ~= 1.1577 Mb of free space.

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My 5.25 disks are new old stock Verbatim disks which I can read and write to no problem but I do not have any other 5.25 disks besides these to test. I still have the box and it says IBM format and 1.6mb unformatted capacity and 1.2mb formatted, so it seems like they are correct...

The keyword is "unformatted". Using special formatters you can get more free space on such 5.25" floppy, creating more tracks (up to 83 or 84), more sectors per track (up to 17 or 18), using non-standard sector sizes, reduced spaces between sectors, variable number of sectors on each track (like IBM XDF does) or even format a disk with variable density (double density for inner and high density for outer tracks). I.e. using 2M utility you can format 1.2M floppy to 1,577,472 bytes. But to be able to read and write your data you'll need special drivers (FDRead, 2M, PU_1700, 800.com etc). Some floppy drives and mainboard bios'es can succesfully work with floppies formatted this way, some others cannot. And storing your data on such floppy isn't as reliable as on a floppy with standard size.


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 Post Posted: Sun Jun 18, 2017 12:44 pm | Post subject: Re: 5.25 disk images?
 
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I tested all 10 of them and the likelyhood of them all having bad sectors is pretty low... I would think. Its good to hear that nothing is wrong with my drive though. I'll try more disk writing programs then. The others I've tried fail at 97% written because it runs out of space... le sigh.


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 Post Posted: Sun Jun 18, 2017 2:35 pm | Post subject: Re: 5.25 disk images?
 
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Use the DOS version of SCANDISK and do a surface scan on each diskette. There should be a graphic screen displaying any bad sectors found. If they haven't got any issues, try WinImage under Windows.

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 Post Posted: Sun Jun 18, 2017 2:49 pm | Post subject: Re: 5.25 disk images?
 
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If it is a problem with air residue, then all 10 of them are, in fact, likely to have the same problem.

And a disk writer can't run "out of space" as you should be writing the entire disk.


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 Post Posted: Sun Jun 18, 2017 2:56 pm | Post subject: Re: 5.25 disk images?
 
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SomeGuy wrote:
If it is a problem with air residue, then all 10 of them are, in fact, likely to have the same problem.

Air residue? Never heard of that. What is it and how does it happen?

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 Post Posted: Sun Jun 18, 2017 3:32 pm | Post subject: Re: 5.25 disk images?
 
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Basically, smoke and air pollution find their way on to the surface of the disks and settle over very long periods of time. Even gets inside sealed boxes.

At least that is one hypothesis, there very well may be other factors.

But it always exhibits the same way. Mainly on high density disks, the the disks appear clean and in good condition, but reading/writing will encounter errors towards the inner tracks. A number of retries will allow the operation to succeed and subsequent read/write operations will eventually allow *perfect* operation.

It is very odd because with most other kinds of read/write errors there is a large risk of causing additional damage while retrying.

Doing data recovery, one normally assumes the condition of the disk will get worse as it spins.


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 Post Posted: Sun Jun 18, 2017 4:33 pm | Post subject: Re: 5.25 disk images?
 
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You guys are the best.

Scandisk did indeed find bad sectors
http://i.imgur.com/QPMQJwd.jpg
http://i.imgur.com/XU8oNUB.jpg

After fixing these I tried WinImage and... drum roll...

http://i.imgur.com/aRk1645.jpg

Perfectly written, no errors, exact matches in size and numbers of files. So glad nothing is wrong with my drive, as apparently it came from a PC AT? That's what the manual says, or at least its PC AT compatible. Only cost $30 off ebay too. Hooray.


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 Post Posted: Tue Jun 20, 2017 9:08 am | Post subject: Re: 5.25 disk images?
 
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Culbrelai wrote:
You guys are the best.

Scandisk did indeed find bad sectors
http://i.imgur.com/QPMQJwd.jpg
http://i.imgur.com/XU8oNUB.jpg


You might try to restore bad blocks by re-formatting those floppies in rebuild mode. Some format utilities can do it, i.e. FFormat. If it's not a physical damage, you have a good chance to get the full capacity back.


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