Path: utzoo!attcan!uunet!tektronix!tekcrl!tekgvs!toma
From: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 16 bit cards vs 8, SHAFTED?
Message-ID: <4710@tekgvs.LABS.TEK.COM>
Date: 1 Mar 89 16:55:46 GMT
References: <37020@tut.cis.ohio-state.edu> <14313@bigtex.cactus.org> <3778@peora.ccur.com>
Reply-To: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 30

In article <3778@peora.ccur.com> joel@peora.UUCP writes:
>Another thing I'm wondering about is whether a 16 bit card card will
>actually faster than 8 bit cards for most cases. 

Well, if you are going through the BIOS, your won't see any improvement.
I have made the following observations:

1) Code can be written to take advantage of 16 bit access in text mode, since
each character is 16 bits (8 bits attributes, 8 bit character value).  FOr
instance, NANSI.SYS writes 16 bits at a time.

2) At least some of these cards (the Video Seven card I have, for example)
don't insert wait states.  This card runs at bus speeds, while the old EGA
cards I have used inserted about 1usec of wait states with each byte.  This
gives a speed improvement even with 8 bit accesses.

3) Most text applications are not display speed limited, and thus won't show
much speed improvement by the clock, but they sure look lots faster since a
page of text snaps instantly to the screen.  The faster the processor (I have
a 20Mhz 80386), the more important a fast display card is and the more speed
improvement you will see.

4) Speed improvement in graphics modes is less since you cannot do 16 bit
graphics manipulations.  IBM, in their infinite wisdom, used a "Big endian"
display bit ordering in a "Little endian" processor environment, so all
pixel operations need to be done on bytes anyway.

Tom Almy
toma@tekgvs.labs.tek.com
Standard Disclaimers Apply