INT 10H 4f05H - Query/Set SuperVGA Video Memory Window
Expects: AX 4f05H
BH SubFn number: 00H = Select memory window
01H = Query current memory window
BL window ID 0 or 1
DX (subfn 00H only) window position (see below)
Returns: AX VESA status: AH=0 means successful (else failed)
AL=4fH means function supported
DX current or new window position (see below)
Info: This function is used to map chunks of video memory into CPU
address space, or to find out which part of video memory is
currently available to the CPU.
The CPU address space for most systems is the 64K starting at
a000:0. Even in standard VGA modes, there are 256K of video
memory to be accessed. SVGA modes can require 1.3 MB (1280K) of
video memory or more.
For instance, in order to access graphical scan line 1024, you
need to page-in the 20th page of video memory. This function
provides the interface to do that--and avoids needing to the port
I/O or other obscure coding.
Before using this function, you must use INT 10H 4f01H to obtain
a SvgaModeInfoRec containing detailed information about the video
mode. For instance, the rWinBAttrs bit 1 will be 0 if only one
video window is supported for that mode. It also returns
wWinGran, which is essential to determining what scan line gets
pages in when you select a block with DX (see below).
DX with subfn 00H, DX selects the chunk of memory that you want to
DX is a video memory address, expressed in "window granularity
units". The size of such a unit is given in the wWinGran field
of the SvgaModeInfoRec.
For instance, if wWinGran is 4, then the units are 4K, so
addressing a scan line that begins at video memory offset 8193
will require that DX be set to 2 to map in the third page of
This call maps the specified page to the start of the video
memory segment for the specified window. The wWinASeg of
SvgaModeInfoRec will provide the segment address in CPU terms
Notes: ■ This function can also be called via a FAR CALL, to avoid the
INT-handler overhead. Use INT 10H 4f01H to obtain the address
of the function handler.
When called directly, the value in AX is ignored, but other
parameters are the same. Upon return, AX and DX are destroyed.
■ Also note that the function address may change when you switch
video modes, so be sure to obtain the right address, just
See Also: SVGA
VESA/SVGA BIOS Services