On 12/09/16 12:16, Gavin Flower wrote:
[...]
two blocks would be logically adjacent (which means they are likely
to be physically close together, but not guaranteed!).
[...]
Actual disk layouts are quite complicated, the above is an over
simplification, but the message is still valid.
There are various tricks of disc layout ( & low level handling) that can
be used to minimise the time taken to read 2 blocks that are logically
adjacent. I had to know this stuff for discs that MainFrame computers
used in the 1980's - modern disk systems are way more complicated, but
the conclusions are still valid.
I am extremely glad that I no longer have to concern myself with
understanding the precise low stuff on discs these days - there is no
longer a one-to-one correspondence of what the O/S thinks is a disk
block, with how the data is physically recorded on the disc.
Cheers,
Gavin
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