Previously Bob Willard wrote:
Anthony Paul wrote:

Hello Arno, thank you for replying!

Really? Hmmm... so is the only purpose for the mapping itself just for
defect control? And does anyone have any links to a site that explains
how this works on a low level? It's just out of curiosity.

Thanks!

Anthony

Arno Wagner wrote:

Very simple, the mapping between the outside block address and the
physical block placement on the disk is allmost 1:1. Other mappings
are only used for defect replacement and that will affect onlt an
insignificantly small number of blocks.

Arno



HD designers use several strategies for sector replacement, and they
generally treat their choices as proprietary information (trade secrets).

One common scheme is the sliding-sector, in which tracks have hidden sectors
at the "end" of the track. If a defect-free track holds logical sectors
ItoK in physical sectors ItoK and the HD decides that physical sector J is
bad (IJK), then after allocating a hidden sector, logical sectors ItoJ-1
will be in physical sectors ItoJ-1, and logical sectors JtoK will be in
physical sectors J+1toK+1. Yes, Virginia, it is a tad more complicated
than that; OK, maybe a *lot* more complicated.

That would be sort of the pool idea, with the pool resticted
to one track. Easier to implement, but more wasteful.

Arno