This is the explanation from Beau Hollis at LM:

https://www.prepar3d.com/forum/viewtopic.php?f=6312&t=136873&p=212507

1) Windows uses the GPU for the operating system and other applications. Windows 10 provides each application a memory budget. We don't have any direct control over the budget. It may go up or down depending on what else you are doing on your system. It's the app's responsibility to stay under budget.
2) We will continue to work ways to avoid going over budget. For certain UI settings like terrain, and advanced atmospherics, we can predict memory usage well, because we control the number and size of all textures and buffers used by those features. For the general sim, it's hard to do because it is very content dependent. Every model and texture added to the scene takes GPU memory. Compressed 4k textures take up 16MB each which can add up really fast.
3) DirectX11 allows applications to go over budget and the driver then attempts to shuffle resources on and off of the GPU to keep the app running. This tends to cause major performance issues, so it was always best to stay under budget, It just wasn't clear in Dx11 what your budget was or how much was in use. DirectX12 drivers don't allow apps to go over budget, but we do get clear information on memory usage. We've added this data to the InfoGen text to help users tune their settings and content. Our focus for 5.0 was to optimize performance under the assumption that settings and content are tuned to keep the app under budget.
Thanks

Beau Hollis
Prepar3D Software Architect

It is because of how VRAM is managed in DX12.  DX11 managed VRAM allocation, DX12 opens it up and lets the application control it.

My 11GB 1080Ti gets easily maxed out in v4.5 in areas with high resolution and high density scenery (think Orbx Honolulu).  The worst part is that one is not aware of the issue until you suddenly get a slide show.  I now keep HWInfo64 always running just to keep an eye on my VRAM usage, which in v4.5 averages 4 GB just cruising over Canada.  No way am I buying a new video card with less that 11 GB and I'm waiting for something closer to 18-22 GB.

6 minutes ago, downscc said:

It is because of how VRAM is managed in DX12.  DX11 managed VRAM allocation, DX12 opens it up and lets the application control it.

My 11GB 1080Ti gets easily maxed out in v4.5 in areas with high resolution and high density scenery (think Orbx Honolulu).  The worst part is that one is not aware of the issue until you suddenly get a slide show.  I now keep HWInfo64 always running just to keep an eye on my VRAM usage, which in v4.5 averages 4 GB just cruising over Canada.  No way am I buying a new video card with less that 11 GB and I'm waiting for something closer to 18-22 GB.

That is an insane development in hardware requirements, if you ask me and it is exactly as I assumed.

The sim is badly optimized, always was. Going DX12 now punishes this as you can go "over budget" in no time with the usual add-ons to make it look acceptable.

 

Well that definately settles it then. As this clearly sounds as if improvements in memory management can't be expected, I will refund and wait for MSF and then upgrade my PC.

Edited April 15, 20206 yr by Farlis

Good to know--this is another reason not to spend yet another $199 on this version.   I'll save it for MSFS and a new GPU then.

I have a 1060 with 6gb VRAM so I'm wondering what it'll be like for me once I get things installed.  We shall see.

I have a 1080 card so I will hold of purchasing v5, anyone advise on xplane with Vulcan if you have the same vram problems.thanks

25 minutes ago, sfgiants13 said:

I have a 1060 with 6gb VRAM so I'm wondering what it'll be like for me once I get things installed.  We shall see.

You will be disappointed, no doubt about it.

1 hour ago, downscc said:

No way am I buying a new video card with less that 11 GB and I'm waiting for something closer to 18-22 GB.

To be honest, I am not sure that 22 GB will give you much protection or future proofing. I saw on the LM site that they never intended for the new weather to be able to support more than a couple of layers of clouds and even at that 4K is going to eat up a ton of VRAM. This almost seems like a big step backwards to me. I have always been a supporter of Prepar3d but I have to wonder if this is not just a nice way to tell most simmers that it is time to part ways and thank you very much. I wonder if it is just that they need this DX12 stuff for commercial sims where eye candy is not as important. I must say at this point I am very disappointed to say the least.

From the first day that a flight sim was developed for the pc, end users have complained about performance. There is no free lunch. As with FSX, more realism translates into more cpu, gpu requirements. It will never change. If you're happy with third party clouds and third party environment on your p3d v 4.5, I see no reason to change, since p3d v5 is not going anywhere but higher in versions as time goes by.

tc

1 hour ago, downscc said:

DX12 opens it up and lets the application control it

The whole discussion makes me wonder how Microsoft will handle that in FS2020, as they might also have to use DX12. They probably have to cope with even more default data. And then on top of that, how much VRAM will be left for Addons, or how many Addons will FS2020 be able to deal with ?

3 minutes ago, mikealpha said:

The whole discussion makes me wonder how Microsoft will handle that in FS2020, as they might also have to use DX12. They probably have to cope with even more default data. And then on top of that, how much VRAM will be left for Addons, or how many Addons will FS2020 be able to deal with ?

I had the very same thought. It will be something to watch for sure.

any issue with vram is purely a p3d issue

12 minutes ago, cannow said:

any issue with vram is purely a p3d issue

I would be interested to know your reason for saying that.

36 minutes ago, shivers9 said:

 I saw on the LM site that they never intended for the new weather to be able to support more than a couple of layers of clouds and even at that 4K is going to eat up a ton of VRAM. This almost seems like a big step backwards to me. I have always been a supporter of Prepar3d but I have to wonder if this is not just a nice way to tell most simmers that it is time to part ways and thank you very much. I wonder if it is just that they need this DX12 stuff for commercial sims where eye candy is not as important. I must say at this point I am very disappointed to say the least.

This is insane if LM actually intended for people to not use more a couple layers of clouds. This and Beau's statement above is just too much. Here's this brand new sim version and oh by the way you really can't use most of it because your hardware won't support it and you'll get a VRAM OOM. We've gone full circle with OOM. To heck with this word not allowed. I had a back and forth with another formum user a few days ago about version 5 and now I'm eating my words because it turns out I think he was right. I'm staying with v4.5. I can't wait to see people try and use the FSL A32x in this version. I hope MSFS doesn't disappoint like this is.

Edited April 15, 20206 yr by B777ER

8 minutes ago, B777ER said:

I had a back and forth with another formum user a few days ago about version 5 and now I'm eating my words because it turns out I think he was right.

LOL Yea I feel your pain. I had a few words with them myself but feeling a little sheepish right now.