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Old 05-06-03, 02:05 PM   #3
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Join Date: Oct 2002
Location: silicon valley
Posts: 1,603

There are only two DACs in GeForce4 GPUs. This means only two displays can be driven simultaneously. Thus, a dual-VGA card can drive VGA+VGA or VGA+TV, but never VGA+VGA+TV.

Likewise a DVI+VGA+TV card can drive only two displays at the same time. Because NVIDIA TV output is always on DAC B, the port that shares DAC B with TV cannot be used with TV. Some VGA+DVI+TV cards can do VGA+TV and others can do DVI+TV, but you'll never find a NVIDIA card that can do VGA+TV also capable of DVI+TV.

What I find really bogus is when a VGA + TV card has both TV and VGA on DACB. I have a number of GeForce2 and GeForce4 cards that can't do VGA+TV because both are on DACB and nothing is connected to DACA.

EDIT here's a post I made a while back to help explain nView.
Some GeForce2 cards support TwinView and some do not support TwinView, depending on how the OEM manufacturer implements the DACs. All GeForce2 class GPUs have two DACs, DAC A and DAC B. Each DAC can drive one analog display. TwinView requires one display on DAC A and one display on DAC B.

A TV port is supported only on DACB for all NVIDIA GPUs. If an OEM puts an SVideo, RCA, or VIVO connector on a card, it is invariably on DAC B.

A VGA port is supported on both DAC A and DAC B. If the manufacturer provides a VGA port on DAC A, then TwinView is available using <VGA> on DAC A with <TV or VGA> on DAC B.

If the manufacturer puts a VGA port on DAC B and also a TV connector on DAC B, then output is possible for only one display at a time. This is likely how your hardware is manufactured. No driver can make DAC B drive two displays with different images.

One way to verify whether your card has both TV and VGA ports on DAC B is to check it out on the Windows Display control Panel. If the Advanced control panel for your device has "Device Selection" instead of "TwinView " then both ports are using DAC B.
I used to drive a Heisenberg, but whenever I'd glance at the speedometer, I'd get lost.

Last edited by ricercar; 05-06-03 at 02:23 PM.
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