Sector fill pattern

absence · 19 March 2009, 11:12

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?

StingRay · 19 March 2009, 11:42

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.

thomas · 19 March 2009, 16:57

Quote:

Originally Posted by absence

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.

StingRay · 19 March 2009, 17:24

Right, I missed the "increasing byte" bit. =)

21 March 2009, 17:33

Quote:

Originally Posted by absence

Why not fill with zero bytes?

I think it's in order to prevent electromagnetic field.

prowler · 21 March 2009, 18:34

Quote:

Originally Posted by vein

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?

absence · 21 March 2009, 22:36

Quote:

Originally Posted by thomas

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.

Toni Wilen · 21 March 2009, 22:50

Quote:

Originally Posted by vein

I think it's in order to prevent electromagnetic field.

No. Remember that data will be MFM encoded before writing to the disk.

19 March 2009, 11:12	#1
absence Registered User Join Date: Mar 2009 Location: moon Posts: 366	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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19 March 2009, 11:42	#2
StingRay move.l #$c0ff33,throat Join Date: Dec 2005 Location: Berlin/Joymoney Posts: 6,788	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.

19 March 2009, 17:24	#4
StingRay move.l #$c0ff33,throat Join Date: Dec 2005 Location: Berlin/Joymoney Posts: 6,788	Right, I missed the "increasing byte" bit. =)

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