Basic Disk Operating System (BDOS) Functions
The
Get
Disk Parameter Block Address function returns the offset
and
the segment
base
of
the BIOS resident disk
parameter
block
of
the currently selected drive in BX
and
ES. This control block can be used for two purposes. First, the disk
parameter
values can be extracted for display
and/or
space
computation.
Second, transient
programs
can
dynamically change the values
of
current
disk parameters when the
disk environment changes, if required. Normally, application
programs
do
not
require this facility. (See
Chapter
7 for a definition
of
the BIOS disk
parameter
block.)
SET/GET
USER
CODE
ENTRY
CL:
20H
DL: OFFH (get)
or
User Code
(set)
FUNCTION
32
SET/GET
USER
CODE
RETURN
AL:
Current
User Code
or
(no
value)
The
Set/Get
User Code function performs one
of
two operations, depending
on
the
value in register
DL
when the function
is
called.
It
either returns the
number
of
the
currently active user,
or
it sets a new current user .
• The
Get
function
is
performed
when register
DL
is
set
to
OFFH. The
function returns the value
of
the currently active user (0 - 15) in register AL.
e The Set function
is
performed when register
DL
is
set
to
the currently active
user
number
(0 - 15).
The
function changes the current user
number
to
the
value in
DL
(modulo
16).
No
value
is
returned.
4-23
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