AGP Side band adressing, z buffer and more....

[dbal]

Through my recent transition from a Radeon VE to nVidia GF2Ti I came up with some questions regarding video terms and characteristics that I think many would like to learn about...
First is about AGP side band adressing that my twice powered GF2 doesn't support as reported by Sandra...What does it serve in general regarding 3D performance? When is it enabled and what's better to be in a 3D card? On or Off??
In addition I discovered while running 3D Winmark2001 that I can have only 24bit z buffer selection and not 32 like my ....crippled VE had-strange again thinking the performance rating of the two cards...Another experienced member told me that the GF2Ti supports 32bit but it comes from 24bit z-buffer plus 8bit stencil. Any simpler explanation on that? Is this combination more efficient or the clear 32bit zbp of the Radeon is considered a better feature in terms of real life visual quality?
Thanx in advance for anyone who will take some time to answer me!

 

[BFG10K]

Side band addressing allows AGP to receive/send address information and data requests concurrently with actual data. In terms of performance in 3D games I'd say it's very minimal, if any at all and if there's a difference it'll likely be only in extremely CPU limited situations.

Regarding the Z issue, I don't think the Radeon has a full 32 bit Z either and is instead 24/8 but the driver reports it as 32 bits by simply adding the two figures. There is a driver option in the Radeon's drivers to change how this is reported.

The 8 bit stencil is used for things like shadow maps.

 

[dbal]

Just for the talk of it, the Radeon in the display properties had a drop down menu of selecting the z-buffer values which were 16,24,32 and right next to it was a checkmark in "8-bit stencil" which was on by default. I always had z-buffer in 32bit plus the checkmark on. Maybe the Radeon had 42bit if the driver added the 2 figures but 3DMark sees only the zbuffer that is 32(+8) in Radeon's case and 24(+8) in GF2?

Originally posted by: dbal
.Another experienced member told me that

Oh, btw, I guess u understand that the member I talked about was you,ah? 🙂

 

[ET]

Yes, the GF2 is limited like that. 24/8 (Z/Stencil) is the only 32 bit configuration. Also if you use 32 bit for the display buffer, you'll have to use 24/8 for depth, and if you use 16 bit for display, you have to use 16 bit for depth. The Radeon can mix and match depths.

As for which is better -- the quality difference between 24 bit depth and 32 bit depth is minimal for most applications, so you don't lose much by moving to the GeForce.

The GF2 may be a lot faster than the Radeon VE, but ATI wins on features and quality.

As for sidebanding, I've heard it's only really relevant for AGP x2 and x1.

 

[BFG10K]

Yes, the GF2 is limited like that. 24/8 (Z/Stencil) is the only 32 bit configuration. Also if you use 32 bit for the display buffer, you'll have to use 24/8 for depth, and if you use 16 bit for display, you have to use 16 bit for depth.

Correct and it looks like the GF3 and GF4 might be the same. I'll have to do some more testing to verify this.

The Radeon can mix and match depths.

A full 32 bit Z buffer + 8 bit stencil with the ability to mix and match buffer sizes is a very nice feature.

24 bit depth and 32 bit depth is minimal for most applications, so you don't lose much by moving to the GeForce.

At same time you have to give a slight nod to ATi for this.

but ATI wins on features and quality.

Overall I'd say the Radeon has a higher image quality than the GF2 although nVidia wins with trilinear filtering and the ability to force DXT3 instead of DXT1 in the drivers. Also nVidia's drivers generally boast higher rendering accuracy and correctness than ATi's do.

As for sidebanding, I've heard it's only really relevant for AGP x2 and x1.

Sidebanding works for all current AGP speeds and will likely work for AGP x8 too.