Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!evax!utacfd!letni!texsun!alanya!lupe From: lupe@alanya.Germany.Sun.COM (Lupe Christoph - Sun Germany Consulting - Munich) Newsgroups: comp.sys.amiga Subject: Re: Duped!! Message-ID: Date: 16 Oct 90 17:23:20 GMT References: <90284.232257JKT100@psuvm.psu.edu> Sender: news@texsun.Central.Sun.COM Lines: 36 To add my two Pfennigs to this: *Standard* VGA is indeed limited like that. *Non*standard VGA can do anything it wants. There is an attempt called VESA (forgot what it stands for) to help remedy this situation. I believe the highest you can get with 256 colors these days is 768x1024. (I believe. I'm not sure.) If you look at this, you will see a familiar sight: interlace ! The highest non-interlace resolution popular among VGA board makers is 600x800. This runs up to 35.5 kHz horizontal frequency, which is about the maximum the cheaper monitors with VGA (i.e. analog) input and variable synch can handle. The organisation of the PC memory forces the resulting 480.000 bytes to be addressed in "pages". The PC can only address 1024 kByte, and of this 384 kByte are set aside for PROMs and memory mapped I/O. This makes VGA slower than it would need to be. The driver has to be quite clever about switching pages. Talk about 16 MByte address space ! The good thing is that seemingly most VGA boards do not use the plane organisation the earlier boards had and the Amiga still has. I.e. the pixels are not split into single bits with all bit in the same position of all pixels lumped together, but a chunky organisation, i.e. all bits of a pixel stored in a single byte. Have you ever seen plane flicker ? That's when the Amiga moves big chunks of pixels. It has to move them bit plane by bit plane. Sometimes this becomes visible. The good thing about VGA is that there are only a few manufacturers of the VLSI chips needed to build such a board economically. But still these chips allow a big variation in video modes. -- | lchristoph@Sun.COM (Internet) | Disclaimer: | | ...!unido!sunmuc!lupe (German EUNet, "bang") | My employer has a | | lupe@sunmuc.UUCP (German EUNet, domain) | non-exclusive license | | ...!suninfo!lchristoph (Sun Germany customers) | to my opinion. |