# Re: Order of sectors on a track

From: Ruud_at_Baltissen.org
Date: Sat, 23 May 2009 11:06:28 +0200
Message-ID: <4A17D8B4.3955.A553DA@Ruud.Baltissen.org>
```Hallo allemaal,

> Second idea (that just popped up): I only use
> this method for track 25 - 35. Wow, I'm good :)

The idea worked out fine indeed and still only 35 seconds :)
FYI, I check things by using a floppy I created myself. I filled all
sectors with nines (to have something different then the content written by
the format routine) with the exception of the first two bytes: they
represent the track and sector number of that particular sector. After
executing the copy routine, it is just a matter of checking these two
particular bytes on every sector of the harddisk.

But I'm still left with a question: why did things go wrong? My first
thought was that it had to do with the sector density of inner tracks. But
this morning it occurred to me that that idea is wrong! The inner tracks
have less sectors/track then the outer ones, thus less sectors pass the
head/second then in case of the outer tracks. So expecting to find sector
4, with the inner tracks I rather expect to run into sector 3 then sector
5. The only thing that comes into my mind is "intersector distance", the
distance between two sectors.

Writing the above I decided to check things again. I installed a previous
version and started to check what sector from the floppy was loaded and the
order as it was done (interleave = 5):
harddisk  floppy
0          0
5          5
10         10
15         15
2          1
7          6
12         11
17         16
4          2
9          7
14         12
1         17
6          3
11          8
16         13
3          0
8          5
13         10

It seems my previous conclusion was wrong: not the 6th but the fourth
sector is loaded from time to time. What is also strange, it only happens
when I pass the last sector. The only thing that now comes to my mind is
the gap between the last and first sector. Think, think, think.... the
original DOS calculates all gaps but I'm not sure if JiffyDOS does. I
suspect JD uses an hardcoded number, one that should also work on a disk
that turns slower then it should, but within limits. On a normal drive this
will leave a wider gap between the last sector and sector 0. And this is
most probably what I ran into.

--
___
/ __|__
/ /  |_/     Groetjes, Ruud Baltissen
\ \__|_\
\___|       http://Ruud.C64.org

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