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From: dhinds@portia.Stanford.EDU (David Hinds)
Newsgroups: comp.sys.ibm.pc
Subject: Re: VGA curiosity
Message-ID: <11925@portia.Stanford.EDU>
Date: 2 May 90 16:21:17 GMT
References: <11094@bsu-cs.bsu.edu> <1093@ntmtv.UUCP>
Sender: David Hinds <dhinds@portia.stanford.edu>
Organization: Stanford University
Lines: 32

In article <1093@ntmtv.UUCP> urbach@ntmtv.UUCP (Steve Urbach) writes:
>
>Go back to your math book  ;^) . You forgot to includ *ALL* the variable
>in your formula. 640*400 = 256k bits of MONO pixels with atributes.
>To get  all 256 colors you need 256K bytes just for 8 bit color
>atributes plus 8k bytes for pixels and 4k bytes for intensity bit.

    Sorry, go back to your VGA book.  Where did this memory for "pixels"
come from, and what is it supposed to do?  There aren't any intensity
bits in graphics, either.  My VGA card (an ATI VGA Wonder) didn't seem
to have much trouble at 640x400 in 256 colors, with "only" 256K.

>Then there is the *TEXT* mode pages that do not go away in graphics mode
>with their mode bits (flash, underline,intensity, reverse) this takes
>at least 3k bytes per page.

    Sorry, all those text pages DO go away in graphics mode; text and
graphics memory are one and the same on all VGA cards I'm aware of.
    The 640x400/256 mode is not a standard VGA mode, and different
vendors support it in different ways.  The problem is fitting that 256K
of memory into an address space of usually only 64K.  Each card maker
has their own scheme for switching pieces of memory into this address
space.  So, to use this mode, you either need software from your vendor,
or drivers written specifically for your card.
    By the way - I saw an article somewhere about the final specifications
of the Super VGA ROM extension.  Does anyone know if any vendors have
started to support this yet, or have device drivers to do this?  This should
clear up a lot of the problems, and make extended VGA cards vastly more
useful.

 -David Hinds
  dhinds@popserver.stanford.edu