riscy
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Video on the motherboard

To: riscy@pyramid.com
Subject: Video on the motherboard
From: caret@pyramid.com (Neil Russell)
Date: Sat, 3 Jul 93 21:26:46 PDT
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
The question is whether to put the video on the motherboard or not.

Many (most?) of the people interested in this board want to make a
nice fast workstation.  Any good workstation has fast, big colourfull
video.  The issue here is just how do you get that glossy video
and how much to pay for it.

Its true that the video will be the most expensive optional part or
the board, coming in at about $100.  I offer some alternatives.

First, video on the board:

        *  1 MB of Video RAM (supports 1024x1024 8-bits per pixel;
           better resolutions if 1,2 or 4-bits per pixel are used)
                or
           2 MB of Video RAM (supports 1280x1024 8-bits per pixel)
        *  TI 34076 RAMDAC (has pixel multiplexing, 256 out of 2^16 colors).
        *  NSC 1882 (generates Video sync, and DMA requests.?)

If the peripheral controller is a 3730, then special logic would be
provided to generate the shift register load cycles for the VRAM,
and, of course the main CPU does the video support.  If the peripheral
controller is the 3041, then the VRAM may be connected to either
processor.  If it was connected to the main CPU, the 3041 could still
access the VRAM anyhow, albeit a little slower.  The 3041 could
generate the special VRAM cycles.

Advantages of video on the motherboard:
        *  High bandwidth direct connection to CPU
        *  Linear memory organization (good for software)
Disadvantages:
        *  Adds significant cost to the end price of the motherboard.

For those that don't want the video section, the motherboard could
be sold with empty sockets for the whole video section.  A separate
video add-on package containing the chips to plug in could be put
together.


Video on a VESA or local bus connector:

(I understand that VESA and local bus are the same thing; correct me
 if I'm wrong.)

Advantages of VESA video:
        *  High bandwidth direct connection to CPU
        *  Linear memory organization available
        *  Cards available to do this already
        *  No work for us to design video
Disadvantages of VESA video:
        *  CPU is assumed to be an x86 (hard work to connect to a R3000)
        *  VESA is apparently going to die soon.
        *  VESA and its replacement, PCI, require licenses to use.
        *  Higher total cost than motherboard solution


Video on the ISA bus (assuming there is one):

Advantages of ISA video:
        *  Cheapest video solution
        *  ISA easy to implement
        *  Accelerator cards available that support reasonable speed
        *  Almost everyone already has a ISA video card
        *  Software already exists
        *  No work for us to design video
        *  Cards will be around for a while (ISA will not die soon)
Disadvantages of ISA video:
        *  Still not as fast as direct connect video, even with accelerators
        *  Higher total cost than motherboard solution (if using fast card)
        *  Very complicated interface (VGA)


No video at all:

Advantages:
        *  Cheapest solution of all
Disadvantages:
        *  Must have external terminal
        *  Not as cool!


My personal opinion is that the video should be on the motherboard as
an option.  That is, the video designed and tested, but motherboards
shipped with empty sockets.  I'm one of those that want the really cool
huge colour monitors.


Comments?
-- 
Neil Russell            (The wizard from OZ)
Pyramid Technology                      Email:  caret@pyramid.com
3860 N. First Street                    Voice:  (408) 428-7302
San Jose, CA 95134-1702                   FAX:  (408) 428-8845

 

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