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How long is a sector?

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How long is a sector?

Postby bootmaster on Thu Feb 15, 2007 11:43 am

How long is a sector? Not as easy as it sounds ...
I need the answer with high accuracy and in millimeters.
I've searched many pages and they almost all skip this one detail.
I'm using 650mb/700mb CD-R/CD-RW ...
After many articles, I did find 17.33 millimeters
clearly stated, but that just has to be wrong.
I am currently using 15.974 millimeters, it seems close.
I think it must be between 15.93 and 16.23 ...
I think it stays constant thruout a given disc.
Would a 'Zoned Constant Linear Velocity' (ZCLV or P-CAV) drive
mess with the length in mid disc?
I need to know BEFORE the disc is written and I fear
the drive may not select a scanning velocity until
it starts to burn ???
Can anyone shed some light on this?
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Re: How long is a sector?

Postby redk9258 on Thu Feb 15, 2007 8:49 pm

bootmaster wrote:How long is a sector? Not as easy as it sounds ...
I need the answer with high accuracy and in millimeters.
I've searched many pages and they almost all skip this one detail.
I'm using 650mb/700mb CD-R/CD-RW ...
After many articles, I did find 17.33 millimeters
clearly stated, but that just has to be wrong.
I am currently using 15.974 millimeters, it seems close.
I think it must be between 15.93 and 16.23 ...
I think it stays constant thruout a given disc.
Would a 'Zoned Constant Linear Velocity' (ZCLV or P-CAV) drive
mess with the length in mid disc?
I need to know BEFORE the disc is written and I fear
the drive may not select a scanning velocity until
it starts to burn ???
Can anyone shed some light on this?



I am going to take a guess and say the length of the 1s and 0s and thus the sector vary throughout the disc as the speed also changes.
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Variable length sectors huh?

Postby bootmaster on Fri Feb 16, 2007 12:48 pm

I considered this ..
Interesting, can anyone confirm or deny this?
If so;
Burning software could offer extra capacity by pre-reading the data
and discovering an abnormal number of 0's
(I've never seen this)
-and-
An audio CD playing at 1x, at 75 sectors per second,
would continuosly have to change speed to account
for areas with slightly more or less 0's ... Hmmmmm?
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Found one of my sources

Postby bootmaster on Sat Feb 17, 2007 11:57 am

While the variable (physical) length sector may very well be correct.
And I know a player would change speed to track it.
I'm hoping a recorder does not create this situation.
(It probably does)

Here is where I found the Sector length (mm) 17.33
that I did not like so well.
Maybe he is talking audio (no difference?) ...
http://repairlaptop.uw.hu/ch10lev1sec3.html#ch10table02

(I also found 15.974 millimeters specified somewhere, I liked it beter)

And for what it is worth, under 'Constant Linear Velocity'
http://everything2.com/index.pl?node_id=1710229
says;
....It means, though, that a sector of data is always written in the same amount of space on the disk surface....

If physical sector length is variable, wouldn't that make
CD-RW capacity variable?
Wouldn't everybody already know that?
Everyone wants more capacity.
That would (in rare cases) allow a form of overburning
that does not even invade the lead-out area.
They could advertise a 700mb CD-R as 'Up to 720mb'.

My current bet is variable, but thats gonna be
tough and some sources indicate otherwise ...
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Postby Slyfox1 on Wed Feb 21, 2007 2:27 pm

I have also wondered about this even for .vob file, when the files are broken down into sectors what exactly does that mean and how do they calculate a " Sector"?
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Postby Ian on Wed Feb 21, 2007 9:16 pm

It is possible to fit more data on a disc. Plextor's GigaRec and Sanyo's HD Burn technology both do this by reducing the track pitch and the size of the pits and the lands. Does this change the size of the sector? Most likely as you can fit more data in a smaller amount of space.
"Blu-ray is just a bag of hurt." - Steve Jobs
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Here is my current best guess. Any comments? Please ...

Postby bootmaster on Sun Apr 08, 2007 7:27 am

In hopes of a bit of discussion, my current bet is as follows;
Can anyone confirm or deny any of this?

63 minute; 1.4m/s, 1.6 micrometer track pitch, 63.5 micrometer pregroove wobble
Sector length: 18.666mm (May vary 18.533 to 18.799 within a disk)

74 minute; 1.2m/s, 1.6 micrometer track pitch, 54.4 micrometer pregroove wobble
Sector length: 16mm (May vary 15.866 to 16.133 within a disk)

80 minute; 1.2m/s, 1.5 micrometer track pitch, 50.3 micrometer pregroove wobble
Sector length: 16mm (May vary 15.866 to 16.133 within a disk)

With 15.866 and 18.799 being out of spec (1.19m/s and 1.41m/s),
yet within acceptable ±0.01m/s scanning velocity variation per disk,
would they just not happen?

Does any standard CD-R/CD-RW use 1.3m/s, or does that just happen to be a tenth between the two extremes actually used?
I saw 17.33 millimeters listed (see the link I left earlier in this thread).
He is using 1.3m/s in his example for both 70 and 80 minute CDs.
That would give the 17.33, but thats wrong, right?????
Pressed silver CDs maybe?

I've seen 1.1m/s specified also. Out of spec right?

(I'm only talking about the origional 'clasic' formats here.
Not newer stuff that goes well out of the origional specs.)

Also, is it correct that 1's are not longer than 0's, but rather the transition
between a land and a pit or pit and a land ???

At least a couple of members chimed in on this forum,
I had posted the same origional question on cdrinfo forum
and have so far had ZERO responses.
So, by comparison, cdrlabs rules!
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