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From: aep@world.std.com (Andrew E Page)
Newsgroups: comp.sys.mac.hardware,comp.sys.mac.programmer
Subject: Re: NuBus traffic
Keywords: NuBus, ethernet, video
Message-ID: <1991Jun11.190925.25293@world.std.com>
Date: 11 Jun 91 19:09:25 GMT
References: <1991Jun11.160305.7049@hubcap.clemson.edu>
Organization: The World Public Access UNIX, Brookline, MA
Lines: 38

In article <1991Jun11.160305.7049@hubcap.clemson.edu> jlind@hubcap.clemson.edu (james alexander lind) writes:
>Does anyone out there know anything about how much traffic Macintosh
>video cards and ethernet boards cause on the NuBus?  What percentage of
>NuBus bandwidth is used by most video cards and ethernet interfaces?
>15%, 20%, any ideas at all?  Thanks in advance for any info.


   The Mac implementation of NuBus has a maximum bandwidth of 
about 20 MB/second.  Add to that the screen is not really
causing all that much taxing of that when you consider that the
QuickDraw toolbox does not write to the whole screen at once.  
When the mac screen is idle(not even a menubar clock) and
nothing is being written to the screen to change it the
ussage will be down around zero.  Some of the NuBus card drivers
might be performing some periodic updates but that should be 
negligible if it is there at all.  

Wipping out the hp.  A 480x640 screen....at 4 bytes per pixel(32bit QD)
should be... about 1.2 meg of memory.... which will take about
0.0589 seconds to transfer.  THAT IS FOR A FULL SCREEN UPDATE.
Most of the time QD is writing in very small peices.  


Not having an ethernet card (yet) I can't speak for that.  But that
will depend heavily on the traffic going through ethertalk.  Again
there may be perioic maintenance beign done by the card driver.  One
way to check is to get out Macsbug and check the drivers data area.
Considering that the MAXIMUM ethernet can do is 10 megaBITS/second
I doubt hightly that it can get above 5% of the NuBus bandwidth
under the best of conditions.  




-- 
Andrew E. Page (Warrior Poet)   |   Decision and Effort The Archer and Arrow
Concepts Enginerring            |     The difference between what we are
Macintosh and DSP Technology    |           and what we want to be.