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C141-E064-03EN3 - 6
3.1.3 Track format
(1) Physical sector allocation
Figure 3.4 shows the allocation of the physical sectors in a track. The length in bytes of each
physical sector and the number of sectors per track vary depending on the logical data block
length. The unused area (G4) exists at the end of the track in formats with most logical data
block lengths.
The interval of the sector pulse (length of the physical sector) is decided by multiple of
20MHz free running frequency. This clock is not equal to the interval of the byte clock for
each zone. Therefore, the physical sector length cannot be described with a byte length.
Figure 3.4 Track format
(2) Track skew and cylinder skew
To avoid waiting for one turn involved in head and cylinder switching, the first logical data
block in each track is shifted by the number of sectors (track skew and cylinder skew)
corresponding to the switching time. Figure 3.5 shows how the data block is allocated in each
track.
At the head switching location in a cylinder, the first logical data block in track t + 1 is
allocated at the sector position which locates the track skew behind the sector position of the
last logical data block sector in track t.
At the cylinder switching location, like the head switching location, the first logical data block
in a cylinder is allocated at the sector position which locates the cylinder skew behind the last
logical sector position in the preceding cylinder. The last logical sector in the cylinder is
allocated when formatting, and is an unused spare sector.