Hard disk track layout

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Interleave 3

  • Gap1 = 16
  • Gap2 = 3
  • Gap3 = 22
  • Sync = 13
  • Count = 32
  • Size = 2*128

Gap 1

16 x 4e 

Sector 0

13 x 00
IDAM a1 fe | 00 00 00 01 | CRC f1d3 
3 x 4e | 13 x 00
DAM a1 f8 | 256 x e5 | CRC e5b4 
3 x 00 | 19 x 4e

Sector 11

13 x 00
IDAM a1 fe | 00 00 0b 01 | CRC 2d29 
3 x 4e | 13 x 00
DAM a1 f8 | 256 x e5 | CRC e5b4 
3 x 00 | 19 x 4e

Sector 22

13 x 00
IDAM a1 fe | 00 00 16 01 | CRC 5806 
3 x 4e | 13 x 00
DAM a1 f8 | 256 x e5 | CRC e5 b4 
3 x 00 | 19 x 4e
...

Gap 4

340 x 4e 

Gap 4 is actually truncated by the passing index mark.

Size of a track:

  • With a 10 MHz clock for HD, the cell size is 100 ns.
  • With 3600 Rpm we have a track length of 16.6667 ms. This means we have a maximum of 166667 cells.
  • With 16 bit per encoded byte we get 10416 bytes as the maximum (unformatted) capacity.

Size per sector: 319 bytes

All sectors: 10208 bytes

With Gap 1 being 16 bytes long this leaves 192 bytes for Gap 4.


Track 0 0 11 22 1 12 23 2 13 24 3 14 25 4 15 26 5 16 27 6 17 28 7 18 29 8 19 30 9 20 31 10 21
Track 1 0 11 22 1 12 23 2 13 24 3 14 25 4 15 26 5 16 27 6 17 28 7 18 29 8 19 30 9 20 31 10 21
Track 2 0 11 22 1 12 23 2 13 24 3 14 25 4 15 26 5 16 27 6 17 28 7 18 29 8 19 30 9 20 31 10 21

...

Interleave 4

  • Gap1 = 16
  • Gap2 = 3
  • Gap3 = 22
  • Sync = 13
  • Count = 32
  • Size = 2*128
Track 0 0 8 16 24 1 9 17 25 2 10 18 26 3 11 19 27 4 12 20 28 5 13 21 29 6 14 22 30 7 15 23 31
Track 1 0 8 16 24 1 9 17 25 2 10 18 26 3 11 19 27 4 12 20 28 5 13 21 29 6 14 22 30 7 15 23 31

...