phil@ux1.cso.uiuc.edu (07/22/89)
The standard VGA adapter for IBM PC and clones has 256K of memory. I understand this memory is mapped somewhere in the 384K of space between A0000 and FFFFF. Does anyone know where? Now I see enhanced VGA adapters with 512K of memory. Now where would THEY be mapped as there is not that much space. Would they creep up above the 1 Meg line? --Phil howard-- <phil@ux1.cso.uiuc.edu>
vgopal@cbnewsc.ATT.COM (venu.p.gopal) (07/23/89)
In article <5300025@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu writes: >The standard VGA adapter for IBM PC and clones has 256K of memory. >I understand this memory is mapped somewhere in the 384K of space >between A0000 and FFFFF. Does anyone know where? > >Now I see enhanced VGA adapters with 512K of memory. Now where >would THEY be mapped as there is not that much space. Would they >creep up above the 1 Meg line? No. All memory is mapped to the region A000:0 to BFFFF:F. Most cards use page switching / multiple bit plane implementation do limit the address region. Venu P. Gopal UUCP: att!ihuxy!vgopal Internet: vgopal@ihuxy.att.com BITNET: com%"vgopal@ihuxy.att.com" or com%"vgopal%ihuxy@research.att.com" Silence those silent letters, save the world 500 million keystrokes a day.
kensy@microsoft.UUCP (Ken Sykes) (07/25/89)
In article <5300025@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu writes: > >The standard VGA adapter for IBM PC and clones has 256K of memory. >I understand this memory is mapped somewhere in the 384K of space >between A0000 and FFFFF. Does anyone know where? > >Now I see enhanced VGA adapters with 512K of memory. Now where >would THEY be mapped as there is not that much space. Would they >creep up above the 1 Meg line? > >--Phil howard-- <phil@ux1.cso.uiuc.edu> For standard VGA displays the graphics screens in general start at A0000 (i.e. 640x480x16 & 320x200x256.) If you look at the memory map you will notice that only 128K is reserved for video memory. Boards that have more than 128K memory have a few options: - organize the memory as planes (EGA/VGAs do this) - use memory banking. That is, tell the controller which 64K/128K chunk of memory you want and the display maps the chunk to the addressable memory @ A0000 (I think Paradise SVGA does this) Adapters with 512K most certainly have to use some kind of banking scheme. One other note, the memory starting at C0000 is used by one of the ROM chips, so display boards should run into trouble if they go outside their 128K block. Sincerely, Ken Sykes