FreePascal: Identifier not found "MEMW" - freepascal

Question

I am migrating a Turbo Pascal application into Free Pascal 32 bit for Windows 7 operating system. Whenever I compiled unit file in Free Pascal, the compiler shows error message:
Identifier not found `MEMW`.
Can anybody help me on this? My code is shown below, is there any option to implement the same thing?
PROCEDURE window_object.appear;
VAR
width_offset,
height_offset : BYTE;
current_location : location_pointer;
BEGIN
current_location:=first_location;
FOR height_offset:=y TO (y+y_offset-1) DO
BEGIN
FOR width_offset:=x TO (x+x_offset-1) DO
BEGIN
**MEMW[$B800:(width_offset-1)*2
+(height_offset-1)*160]:=current_location^.code;**
current_location:=current_location^.next;
END;
END;
current_location^.next:=NIL;
END;

Answer 1

Access to the DOS screen at $B800 is only possible in DOS versions.
DOS versions are only supported in dosboxes of Win98, so not supported under Windows NT variants like NT4/W2k/XP/w2003,vista,w2008,w7,w8(.1)
In general, code relying on DOS direct screen access schould be rewritten to use the video unit.
The Video unit is platform independent, and maintains a virtual screen buffer. The VideoBuf variable allows direct access to it. Procedural variables can be used to minimize the needed modifications:
Recently I made a simple unit for the TP dialedit program (which is a Turbo Vision application).
For this to work, the main program needs
to call video.initvideo on startup
video.donevideo on shutdown.
Non Turbo Vision programs need to also call updatescreen(false) to update the screen (e.g. as the last line in your function)
The unit:
unit videord;
// emulates three param screen[] array for dialedit.
// can't be in dialedit since procedural properties aren't allowed in $mode tp
interface
uses Video;
function videoreadchar(x,y,z:integer):char;
// Coordinates are 1 based, z=0 gets the character, z=1 gets the attribute.
property screen[x,y,z:integer]:char read videoreadchar;
implementation
function videoreadchar(x,y,z:integer):char;
Var
P: Integer;
begin
P:=((X-1)+(Y-1)*ScreenWidth);
videoreadchar:=pchar(#VideoBuf^[P])[z];
end;
end.