Wise to shut off Secondary Vid/display in Device Mgr.?

[schleppy]

I'm using a Asus 9600xt 128mb and was just wondering if I would gain any performance by shutting off the secondary display in device manager. I'm just using the reg VGA out to 1 monitor, no other monitors..

Any suggestions?

 

[VirtualLarry]

Potentially, yes, since if the RAMDAC is active, it is "stealing" a small amount of memory bandwidth for the refresh of the unused display output. (That depends on the type of memory used on the card too, there won't be a performance hit if it's dual-ported, but many cards use standard DDR so it could give you a tiny (like, 1-3%) performance increase. Actually, that would be very interesting to see, try running 3DMark2001, and bench it both ways, and see what the memory fill-rate/texturing scores are in both cases.

 

[schleppy]

Ya I need to run a few bench marks to see as well, I've tried shutting it off in the vid display properties but no go so I wasn't sure if it was a good idea to disable it in Device Mgr.

Thx for the reply! When I get a chance here, I'll give it a try.

The memory on the card is Samsung.

 

[VirtualLarry]

It's actually far more important if the "other" display happens to be onboard video, and you are using an add-in card. Sometimes, after upgrading to a standalone video, XP still loads the drivers and allows the onboard video to be "active" in the background.

Just some back-of-envelope calculations - assume a R9200SE card, 64-bit mem, 200Mhz DDR (400Mhz effective) clock. That gives you a total theoretical memory bandwidth of 8 x 400 = 3200MB/sec. Now lets assume you have both RAMDACs enabled (dual-head), and both are displaying 1024x768 @ 32bpp displays, at 75Hz. That's 1024x768x4x75 = 225MB/sec, per each display head, for a total of 450MB/sec / 3200MB/sec, or 14% of your card's memory bandwidth going for just display-refresh purposes. Disabling one of the displays/RAMDACs, would cut that overhead in half. Not to mention, that assumes "perfect" memory-access scheduling efficiency, which doesn't happen in the real world. Display refresh is the highest-priority task (otherwise you would get visual anomolies on-screen), and can interrupt/delay other tasks like GPU rendering and host CPU access to onboard video memory, so when you add overhead, that number is higher. I actually didn't think that it was so high, wow, but I did pick what is nearly the slowest card on the market for the example. For something a bit more modern and high-end, the numbers are probably closer to 1-3% like I said earlier.

Interestingly, also, when you consider that a 32-bit 33Mhz PCI bus has only a maximum theoretical bandwidth of ~128MB/sec, and a simple onboard video display will take nearly twice that amount of memory bandwidth, just to keep the screen refreshed, then you start to realize what sorts of overhead to the rest of the system (CPU/memory subsystem especially) the use of onboard video will cause, and why it is commonly so vehemently avoided.

 

[schleppy]

Damn Larry, now that's why these Anandtech/forums rock because it's guys like you with thorough answers. Thx man, now you have all these calculations going through my head lol but thats dead on!

I've tweaked my bios where all onboard is off excect my AC'97 sound (dead sound card this week), vid set to AGP primary.

Thx for taking the time!

Get home later try this out.

 

[schleppy]

I ran 3Dmark 2001 SE demo all 21 benchmarks.

1st run with both primary and secondary enabled : 8941

2nd run with secondary disabled after reboot: 9308


Nice increase, I'll try to run some more benches when i have soem more time.

Ran at 1024 X 768

System Specs:

System Info Version: 2.2
Operating System: Microsoft Windows XP
Processor: AMD ThoroughBred @ 2 GHz
Graphics Card: RADEON 9600 SERIES
Total Physical Memory: 640 MB
Free Physical Memory: 416.61 MB
Motherboard Manufacturer:
Motherboard Model: K7VM2



Description: Primary Display Driver
Manufacturer: ATI Technologies Inc.
Name: RADEON 9600 SERIES
Total Local Video Memory: 128 MB
Total Local Texture Memory: 128 MB
Total AGP Memory: 54 MB
Display Driver: ati2dvag.dll
Display Driver Version: 6.14.10.6483
Driver WHQL Certified: Yes
Max Texture Width : 2048
Max Texture Height: 2048
Max User Clipping Planes: 6
Max Active Hardware Lights: 8
Max Texture Blending Stages: 8
Textures In Single Pass: 8
Vertex Shader Version: 1.1
Pixel Shader Version: 1.4
Max Vertex Blend Matrices: 37
Max Texture Coordinates: 8


Revision: 2.0
Rate: 1x, 2x, 4x (4x enabled)
Aperture Size: 64 MB
Sideband Addressing: supported (enabled)
Fast Write: supported (enabled)

 

[TStep]

Something new learned every day.🙂 I must check this myself, that's a 4% hit (or gain) by doing nothing more than checking a box.

 

[Munky]

Hey, nice catch. Now I'm gonna have to check if it boosts my performance.

 

[xtknight]

Guess us poor 6800 owners are out of luck. At least, I only have one graphics adapter in my device manager, thus there's no other one to disable. Any way to turn off the secondary RAMDAC on GeForce cards? I've always hated wasted resources.

 

[imported_humey]

You will only have 1 gpu in device manager, in your desktop settings set to single device not clone or desktop ext, im sure this is what they mean, by unticking others in checkbox, but i could be wrong, anyhow i use dual display to tv out movies with tv tool using desktop ext so i keep what i see on here and movies on big tv.

I dont get what all the other monitors are apart from default plug and play (my crt) and 1 of monitors being tv connected with s-video, but that leaves another 3 still. (got 4 default monitors in total) + my default plug and play.

 

[xtknight]

Originally posted by: humey
You will noly have 1 gpu in device manager, in your desktop settings set to single device not clone or desktop ext, im sure this is what they mean, by unticking others in checkbox, but i could be wrong, anyhow i use dual display to tv out movies with tv tool using desktop ext so i keep what i see on here and movies on big tv.

I dont get what all the other monitors are apart from default plug and play (my crt) and 1 of monitors being tv connected with s-video, but that leaves another 3 still. (got 4 default monitors in total) + my default plug and play.

My ATI Radeon 9500 PRO card actually shows up as two cards under device manager, one primary and one secondary. I think they mean right clicking the secondary and clicking disable. However, that only works for ATI cards to my knowledge. In nView my 6800NU is set to single display so I guess that's as good as it can get.

 

[darkswordsman17]

Yeah, for some reason ATi sets up theirs so that their cards show up as two. Its weird, but I guess it works.

What were the findings then? Did it help much?

 

[JBT]

Originally posted by: xtknight
Guess us poor 6800 owners are out of luck. At least, I only have one graphics adapter in my device manager, thus there's no other one to disable. Any way to turn off the secondary RAMDAC on GeForce cards? I've always hated wasted resources.

On most of the Nvdia drivers that I have seen there is a check box to only use 1 output. I would assume this is similar to ATI's use of two adapters (primary) and (secondary) in the windows device manager.