Date   : Wed, 21 Mar 1984 14:07:55 PST (Wednesday)
From   : Bicer.ES@PARC-MAXC.ARPA
Subject: Re: Does CPM do deblocking on 128 byte sectors ?

Assuming you are talking about CP/M 2.2, the deblocking is done in the
BIOS, which is system dependent. The portable operating system (BDOS),
doesn't know anything about blocking or deblocking. All it expects is to
be able to read and write 128 byte sectors. So, if the disk is formatted
in 128 byte sectors, the answer to your question is:
       CP/M (BDOS or BIOS) DOESN'T DO ANY DEBLOCKING. THE BDOS NEVER DOES
BLOCKING/DEBLOCKING.
One thing that usually happens is called SKEWING, which is used to
increase disk throughput. The logical sector numbers are skewed by an
amount (usually 6 in 8" SSSD format), so that physical to logical
translation takes place according to a skew table (1,7,13,19,2,8,14,....
MOD23(n)).

If you wish to use a size other than 128 bytes, then you have to modify
your BIOS to do blocking and deblocking. The BDOS will not know the
difference.

Jack Bicer