|After my short theoretical essay about AGP the practical
part is following now. It is meant to explain how to use AGP on current
systems and what performance advantage it really gives us. The Intel 440LX
chipset is released now and many people are looking into buying motherboards
with this chipset. After buying a board that supports AGP, you obviously
want to be able using it.
The Software Issue
Although neither Windows 95 nor Windows NT 4 were ever
designed for the usage of AGP, you are certainly able to run both operating
systems on Intel 440LX boards inclusive AGP graphic cards. It takes a little
bit more however if you want to take advantage of this new bus.
First of all we have to remember that AGP in one
way is just an extension of the PCI specifications 2.1. This means that
AGP can be dealt with as if it is another PCI slot. Therefore in most cases
AGP graphic cards can be dealt with via the same driver as for the corresponding
PCI card. In case of the Diamond Fire GL Pro you just have to install the
Windows 95 and Windows NT 4 drivers once and can work with both cards AGP
or PCI. Neither Windows 95 nor Windows NT complain in any way if you should
just swap the AGP card with the PCI card or vice versa. This is good news
for all people that were afraid that their OS wouldn't work with AGP.
Taking advantage of AGP's DIME (Direct Memory
Execute, see "AGP
- A New Interface for Graphic Accelerators") however is somewhat
more difficult. DIME needs to allocate some system RAM via the OS to access
large textures via AGP outside the local graphic memory of the card. The
OS has to know what it's doing and hence definitely needs an extension
that enables this procedure. Unfortunately there isn't any such extension
available for Windows NT 4 yet, but if you realize, that NT is currently
anyhow not the right platform for playing 3D games (no Direct3D support,
only DirectDraw and others with SP3) you will understand why NT users will
have to wait for a decent AGP implementation until NT 5 is released. For
the majority of users however which are using Windows 95 (especially for
games) there are three things necessary:
After setting up your Windows 95 with these things your
system is ready for taking advantage of AGP's DIME feature.
if you are already running Windows 95 OSR 2.1. You will need the
program "USBSUPP.EXE" from Microsoft, which includes the USB supplement
and a new memory manager (VMM32.VxD) needed for the AGP DIME feature.
from Microsoft. DirectX5 is the first DirectX version that supports AGP's
The graphics card vendor should supply you with a virtual
device manager called "VGARTD.VXD", which usually will be installed
in the installation procedure of the Windows 95 card driver. This virtual
device manager is the key to the DIME feature, without it your AGP card
is unable to use DIME. As the name says, "VGART" stands for Virtual GART
Driver, where GART is the Graphics Address Remapping
Table you know about from reading "AGP
- A New Interface for Graphic Accelerators".
The Performance Issue
The expected increase in system performance is certainly
the most interesting thing to all of us. This question can be answered
fairly simple in the first place - there doesn't seem to be any!!! Shocking!!
Well, it isn't quite like that, but you have to try hard finding any improvement
in performance from using AGP. Using any real world applications or benchmarks
won't get you anywhere. It is difficult to believe, but any popular benchmark
program will show you the same results with the PCI card as well as with
the corresponding AGP card. As to my knowledge there is currently only
one benchmark available that can show you the advantage of AGP and its
DIME feature, which is the 3D
Winbench 97 from Ziff-Davis. Now hold your horses before you start
benchmarking with 3D Winbench, because if you are using the benchmark just
as it comes, it won't show you any difference between PCI and AGP either.
What you will need in addition to 3D Winbench is a special scene called
"Station 2 Large Textures Scene". This scene can be downloaded from ZDLabs
This "Large Scene" got its name because it's using very large textures
of up to 6.1 MB. Even new cards with 8 MB onboard memory won't be able
to hold the complete textures in their local (onboard) RAM in case you
are using high resolutions that need a lot of local memory for frame buffering
and Z-buffering.This means that the texture has to be swapped to local
memory. Here is where DIME comes in for AGP cards that are able to use
it. You can see a benefit of about 200% by using the AGP card, when
running the "large scene" at a resolution of 1024x768. The benefit
from AGP decreases whilst using lower resolutions and depending on the
amount of local card memory the results will finally be the same at some
low resolution, e.g. 640x480 in case of a 8 MB graphic card.
You invoke the "large scene" by selecting 'user scene'
in the 'test settings' of 3D Winbench 97. Select 'Stations2LargeTextures.scene'
as user scene name and tick the options you want to run the test with.
Choose the resolution you want to run the test at and run the test via
'selected' in the 'Run' menu, choosing '3D Scene/User Defined'.
To summarize the findings regarding system performance
with AGP graphic cards compared to the corresponding PCI graphics card
there are the following things to be considered:
I can say that so far there is no real world application
available that benefits from AGP's DIME feature.
Normal applications, like e.g. business applications
don't benefit from AGP at all. In Winstone 97 the Business as well
as the HighEnd benchmark are showing identical results between
AGP and corresponding PCI card.
Current 3D applications are also not benefiting from
AGP. The textures used by current 3D games and 3D benchmarks are either
not large enough or the games and benchmarks don't run at high enough resolutions
for forcing the graphic card to swap parts of the textures outside their
local (onboard) RAM into main memory.
As new graphics cards are coming with more local (onboard)
RAM, the textures can get larger than used currently and still fit into
the local RAM. Only applications that use particularly large textures
or graphic cards with only 4 MB local RAM or less will see an advantage
from AGP, at least for now.
If you want to see some hard numbers which prove
the above said, please use the following link:
Comparison PCI vs. AGP