andras@alzabo.uucp (Andras Kovacs) (01/06/91)
Does someone know why the maximum ScreenSize is limited to 480K? It means
that one cannot double-buffer bigger than 240K screens (mode 21/24/28).
Please reply by E-mail if you feel that the problem is a silly one...
Thanks!
--
Andras Kovacs "Could somebody tell me what kind of a world we live in
andras@alzabo.UUCP where a man dressed as a BAT gets all of my press..."
Nepean, Ont. The Jokerpeterl@ibmpcug.co.uk (Peter Leaback) (01/08/91)
> Does someone know why the maximum ScreenSize is limited to 480K? It >means that one cannot double-buffer bigger than 240K screens (mode >21/24/28). The MEMC can only DMA out of the bottom half meg of physical ram, so a 480K limit is to allow for cursor and sound DMA as well. It is a great shame that the MEMC has this limit, and as you say, one can't double-buffer large screens. What would have been nice would be if the address generators could take logical addresses, so one could play around with the memory map. But this would mean extra logic. Regards,Pete Leaback. . -- Automatic Disclaimer: The views expressed above are those of the author alone and may not represent the views of the IBM PC User Group. --
ecwu61@castle.ed.ac.uk (R Renwick) (01/08/91)
In article <1991Jan6.150113.15268@alzabo.uucp> andras@alzabo.UUCP (Andras Kovacs) writes: > > Does someone know why the maximum ScreenSize is limited to 480K? It means >that one cannot double-buffer bigger than 240K screens (mode 21/24/28). >Please reply by E-mail if you feel that the problem is a silly one... > Thanks! >-- There has been a discussion about this before on the net regarding screen banking. You probably just missed that one. The VIDC chip itself has to be able to access the screen memory as this is obviusly part of it's job. There has to be a limit on the amount of memory it can access just as there is a limit for any machine architecture, the limit for the VIDC happens to be 480k which means that there is no way the current VIDC chip can access more this. Rik