Al parecer se trata de un desplaamiento de pagina:
Inp.:
AH = 06h
AL = number of lines by which to scroll up (00h = clear entire window)
BH = attribute used to write blank lines at bottom of window
CH,CL = row,column of window's upper left corner
DH,DL = row,column of window's lower right corner
Note: affects only the currently active page (see AH=05h)
BUGS: some implementations (including the original IBM PC) have a bug which
destroys BP
the Trident TVGA8900CL (BIOS dated 9/8/92) clears DS to 0000h when
scrolling in an SVGA mode (800x600 or higher)
SeeAlso: AH=07h,AH=72h,AH=73h,AX=7F07h,INT 50/AX=0014h
Copied from Ralf Brown's Interrupt List