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Is possible rebuild a cut floppy disk & retrieve data?

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(@williamsonn)
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Hello

Is currently possible in practice to rebuild a cut in many -more or less symmetrical- pieces a an old floppy disk and retrieve information?

 
Posted : 16/01/2013 5:23 pm
keydet89
(@keydet89)
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It's been possible since the '90s
http//www.csoonline.com/article/219226/computer-forensics-investigations-body-of-evidence

 
Posted : 16/01/2013 5:36 pm
(@williamsonn)
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Very interesting article!! Thanks wink

 
Posted : 16/01/2013 6:08 pm
(@mscotgrove)
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With a floppy, each sector is self contained, and disk drives are 'dumb'. A standard disk drive will therefore work (see note below on CDs)

There may be issues with the data going out of sync (clock and data bits) about the join but as disks store so little data, manual reconstruction is not impossible. Text should be easy to recover - a Zipped file rather harder as there will be errors.

You may need hardware to do a raw track read

With a CD/DVD the reading drive is normally too intelligent and so often stops you processing a partial/badly damaged CD with a 'standard' drive.

 
Posted : 16/01/2013 6:16 pm
(@williamsonn)
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After reading the article, I am thinking now about other, more particular and perhaps more difficult question If instead the entire cut floppy disk (all cut fragments were there) the researcher has only 3-4 remnant cut pieces from a floppy disk(or a few of them) around 1cm x 0,5cm each Can be read something from these? roll ?

 
Posted : 16/01/2013 6:17 pm
(@mscotgrove)
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After reading the article, I am thinking now about other, more particular and perhaps more difficult question If instead the entire cut floppy disk (all cut fragments were there) the researcher has only 3-4 remnant cut pieces from a floppy disk(or a few of them) around 1cm x 0,5cm each Can be read something from these? roll ?

Realistically this is not readable.

To read a track it is easiest to spin the media at the correct speed in a drive. For that ideally you require a fragment that references to either the edge or centre of the disk. That way you stand a chance of reading the data with a standard disk drive.

To read your fragments would require some kind of microscrope to pick each data transistion.

A 1 cm length is also very short. For a 3.5" disk, the outside track is approx 22cm long, and this contains 18 sectors. The chance of a full sector (with address) is low in a 1cm length. Don't forget a floppy records transistions and not absolute 0s and 1s. It is a series of clock and data bits, on double density disks, there is not always a clock bit.

 
Posted : 16/01/2013 9:24 pm
PaulSanderson
(@paulsanderson)
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on double density disks, there is not always a clock bit.

You sure about this? Single or double density the encoding is still MFM (assumimg a PC and not GCR on a Mac) and MFM calls for clock bits always. It's been a long time since I read a floppy at the raw level but I dont recall any difference in the way I read and pieced together double/single density disks.

 
Posted : 16/01/2013 9:57 pm
(@mscotgrove)
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on double density disks, there is not always a clock bit.

You sure about this? Single or double density the encoding is still MFM (assumimg a PC and not GCR on a Mac) and MFM calls for clock bits always. It's been a long time since I read a floppy at the raw level but I dont recall any difference in the way I read and pieced together double/single density disks.

It has been a long time too for me working on floppies - the following is from memory.

Single density ALWAYs has clock bit

MFM has a clock bit if there is no precceding data bit or following data bit - I think

M2FM was slightly different logic, but along the same lines where clock bits were added if there were no data bits. I think Intel were the only people who ever used M2FM

GCR was often 5 bits of disk data for 4 bits of actual data - make sure there were never more than 2 zeros in a row.

400K/800K Macs were GCR, but with 5 different recording rates for each group of 16 tracks.

Sirius and Commodore were all GCR, and some Commodore were 100tpi

 
Posted : 16/01/2013 10:31 pm
PaulSanderson
(@paulsanderson)
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A very quick bit of googling - I think you may be on about MMFM dropping the odd bit. I am pretty certain that both single density and double density floppies used standard MFM - it was just packed in twice as densely (stating the obvious).

 
Posted : 16/01/2013 11:49 pm
(@mscotgrove)
Posts: 938
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I disagree

Only SD always has a clock bit

 
Posted : 17/01/2013 4:03 am
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