New features
Still, some of
the new features seem quite interesting for 3D games. One of them is the new AGP 8x mode, which increases the effective bandwith up to 2.1 GB/s.
This feature, however, has to be eyed with suspicion, recent tests show that
modern games don't even benefit from AGP 4x.
Another significant change is the the signal-reduction from 1.5V down to 0.8V, which is a decrease of 47 %. One might
remember the trouble, the reduction from 3.3V (AGP 1.0) to 1.5V (AGP 2.0) caused
on some motherboards with certain video cards. An AGP 2.0 compatible motherboard
doesn't have to care about 3.3V signaling at all. However, thanks to the universal
AGP motherboard standard (part of the AGP 2.0 specification), support was added.
Universal AGP motherboards support both, 3.3V and 1.5V signaling.
But lately, motherboard manufacturers stopped to implement this standard, meaning
that video cards using 3.3V signaling are not supported anymore. Due to the
fact, that AGP 1.0 video cards havn't been around for years, this shouldn't
cause any trouble. However, some AGP 1.0 compatible video cards using 3.3V signaling,
have been sold as AGP 2.0 compatible and alrealdy destroyed dozens of motherboards.
In order to prevent operation other than AGP 0.8V, Intel now specified an additional
electrical ID for AGP 3.0 compatible slots and motherboards. However, the specification
doesn't make any statement about using video cards with AGP 3.3V signaling in
an „Universal 1.5V AGP 3.0 motherboard“, supporting 1.5V and 0.8V
signaling. Eventually, it's not clear whether AGP 3.3V video cards can cause
major damage to „Universal 1.5V AGP 3.0 motherboards“
Speaking of AGP 3.3V: Since this almost antique signaling hasn't been officially supported since
AGP 1.0 and hasn't been used by video cards for a long time (the last know artefacts
are the SiS315 and few nVidia TNT2 video cards), Intel completely removed it
from the AGP 3.0 specification. Still, motherboard manufacturers do have the
possibility to implement the „Universal AGP 3.0 motherboard“ standard,
in order to re-add support for those video cards. Additional information about
the compatibility between AGP 2.0 and AGP 3.0 can be found in the eponymous
chapter later on.
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