RANA Systems Elite Controller, User Manual

Page: 294 / 328

ELITE SERIES USER MANUAL APPEN. A - DISK I/O
Probably, at least one sync byte will be des-
troyed when writing a Data field because, just
as in reading bits on a track, the write may not
begin on a byte boundary, thus altering an ex-
isting byte. See first figure below.
A . 5 . 3 . G a p 3
This appears after each data field and before
each address field. Though it is similar to Gap
2, it is longer, generally ranging from 14 to 24
bytes in length. It allows the additional time
necessary to handle the data before the next
sector is read.
The length of this Gap is not as vital as that
of Gap 2 because the DOS can always wait for
the next spin under the read/write head if the
address field has been missed, a maximum one
turn of the diskette. Since address fields are
never rewritten, there is no problem with this
gap providing sync, because only the first part
of the gap can be overwritten or damaged, as
demonstrated in the second figure.
The address field contains the ‘address’ or
identifying information about the data field
which follows it. The volume, track, and sector
number of any given sector can be thought of as
its address. The third figure gives a more de-
tailed illustration of its components.
P a g e A - 2 3