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Old 19 March 2009, 10:12   #1
absence
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Sector fill pattern

Several times I've seen unused sectors of a floppy filled with a repeating four-byte pattern consisting of three constant ASCII letters and an byte that continually increases. Examples are "DOS\x00DOS\x01DOS\x02DOS\x03" or "RNC\x00RNC\x01RNC\x02RNC\x03" and so on. Do patterns like these serve a purpose? Why not fill with zero bytes?
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Old 19 March 2009, 10:42   #2
StingRay
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Such patterns are often used to mark unused areas of the disk and as kind of "trademark". When I create disk images I use "STR!" as fill pattern f.e. =)
RNC = Rob Northen Computing, used in games protected by Rob Northen's Copylock.
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Old 19 March 2009, 15:57   #3
thomas
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Several times I've seen unused sectors of a floppy filled with a repeating four-byte pattern consisting of three constant ASCII letters and an byte that continually increases. Examples are "DOS\x00DOS\x01DOS\x02DOS\x03" or "RNC\x00RNC\x01RNC\x02RNC\x03" and so on. Do patterns like these serve a purpose? Why not fill with zero bytes?

It's not three constant letters and a number, it is one 32bit number which is constantly increasing. Which means after DOS\xff comes DOT\0 and so on. The Format command does this. Don't know why. Perhaps they thought a pattern different from 0000 is better to check for bit errors.
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Old 19 March 2009, 16:24   #4
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Right, I missed the "increasing byte" bit. =)
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Old 21 March 2009, 16:33   #5
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Why not fill with zero bytes?
I think it's in order to prevent electromagnetic field.
 
Old 21 March 2009, 17:34   #6
prowler
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I think it's in order to prevent electromagnetic field.
If this is the primary objective of filling the disk with a code pattern, then wouldn't alternating 1s and 0s be the best solution?
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Old 21 March 2009, 21:36   #7
absence
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It's not three constant letters and a number, it is one 32bit number which is constantly increasing. Which means after DOS\xff comes DOT\0 and so on. The Format command does this. Don't know why. Perhaps they thought a pattern different from 0000 is better to check for bit errors.
Actually, on the disk I was examining, DOS\x00 came after DOS\xff.
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Old 21 March 2009, 21:50   #8
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I think it's in order to prevent electromagnetic field.
No. Remember that data will be MFM encoded before writing to the disk.
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