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APPENDIX
~
MDOS 3.00 Differences
9.
FOUT
new
system
functions
have
been pTovided
ror
multiple
sectoT physical
diskette
I/O.
These
ne~
functions
aTe
described
in
sections
25.2.7
and
25.2.8.
The existing system functions have
not
had
theiT function numbers changed.
10.
The
device
independent
1/0
functions (Unified 1/0
functions in previous versions
Or
MDOS
manuals)
¥or
accessing
the
diskette
have been enhanced with the
multiple sector
lID
capability.
Now,
a sector buffer
can
be
larger
than
a
single
sector
in
orde~
to
minimize the number of diskette accesses that must be
made
(and
therefore
decrease the amount of time it
takes a program
to
run).
The
following
areas
have
been affected:
loess!'
the
IOCB sector buffer internal pointer,
is
now used.
This pointer indicates the
end
of
valid
data
within
the
user's
sector
buffer.
It
is
initialized by the . OPEN function to point to the end
of
the sector buffer (IOCSBE).
It is changed by the
input functions to reflect the end of the valid
data
<if only using a single sector,
rOeSSI will always be
the
same
as IOeSBE).
IOCSBEJ
the IOeE ending sector bur-rer pointer,
still
points
to
the
last
b~te
in
the
sector
buffer;
however,
the sector buffer can be an integral
number
of sectors in length (one or more).
No program modification will be required if
a
program
is using record
1/0
and if the sector buffer stays in
the
same
place;
however,
changing the size of the
sector bUTfer should speed up the program.
Programs using logical sector
1/0
will
not
require
modification
if only a single sector is accommodated
b~
the buffer and if the sector burfer is
always
in
the
same
place.
Thus,
existing programs should be
minimally impacted.
If
the
sector
buffer
changes
locations (single sector size),
then the IOeSBI entry
must be adjusted
along
with
the
IOeSBE
entry
to
reflect
the
end of the valid data within the sector
buffer.
If the
user
supplies a sector
bu~fer
larger than
one
sectoTI
then
he
must
realize
that after a .GETLS
function,
he may have more sectors in the buffer than
Just
the
logical
sector
number requested.
IOCLSN
will be updated to point to the logical sector to
be
read
next (incremented
by
the number of sectors that
were read into the buffer).
Upon
return
from
the
. GETLS calli
IOeSB! will point to the last valid data
byte within the sector buffer (less than or equal
to
Page
~-03
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