DBI Output for AGP Trans.
Common Options : Enabled, Disabled
Quick Review
The full name for this BIOS feature is Dynamic Bus Inversion Output for AGP Transmitter. It is an AGP 3.0-specific BIOS feature which will only appear when you install an AGP 3.0-compliant graphics card.
When enabled, the AGP controller is allowed to use the Dynamic Bus Inversion scheme to reduce power consumption and signal noise.
When disabled, the AGP controller will not use the Dynamic Bus Inversion scheme to reduce power consumption and signal noise.
The AGP bus has 32 data lines divided into two sets. Sometimes, a large number of these data lines may switch together to the same polarity (either 1 or 0) and then switch back to the opposite polarity. This mass switching to the same polarity is called simultaneous switching outputs and it creates a lot of unwanted electrical noise at the AGP controller and GPU interfaces.
To avoid this, the AGP 3.0 specifications introduced a scheme called Dynamic Bus Inversion or DBI. It makes use of two new DBI lines - one for each 16-line set. These DBI lines are only supported by AGP 3.0-compliant graphics cards.
Dynamic Bus Inversion ensures that the data lines are limited to a maximum of 8 simultaneous switchings or transitions per 16-line set. It does so by switching the DBI line instead of the data lines when the number of simultaneous transitions exceeds 8 or 50% of the data lines. This ensures that electrical noise due to simultaneous switching outputs are minimized.
In short, DBI improves stability of the AGP interface by reducing signal noises that occur as a result of simultaneous switching outputs. It also reduces the AGP controller's power consumption.
Therefore, it is recommended that you enable DBI Output for AGP Trans. to save power as well as reduce signal noise from simultaneous switching outputs.
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