Question regarding clarification of shared RAM on M1 Machines.

[davedirect]

Recently I read that ram is shared between the CPU and GPU on M1 processors. Does this mean that some of my ram will be allocated to driving an external display? Wouldn’t the GPU have its own dedicated vram so that it wouldn’t cut into ram allotted to the cpu?

32GB of ram is what I currently need for my upcoming purchase, but that was under the pretense of buying a machine with an intel or amd chip and a dedicated graphics card, which I feel like I understood a little more clearly. Now I’m not quite clear on how much of that 32gb ram would truly be available to run non graphics related tasks like I am intending, with an M1 pro processor.

Could any of you offer some clarification on how exactly RAM is used in these Apple silicon machines? I would like to not eat into my available ram by running an external monitor off of my MacBook Pro, but running an additional screen is absolutely necessary for my workflow.

Thanks in advance

 

[Sanpete]

It's all shared RAM, none dedicated only to the GPU. But I don't think driving an external monitor will require much of it. There's a lot of discussion about RAM use and how much people need here:

PSA: you probably don’t need 32 or 64Gb RAM unless you know you need it.

With the new MBPs, this question is super-popular on these forums, and I see multiple posts spreading misinformation and FUD about 16Gb models, causing a bunch of people to most likely overspend of panic about their purchases. There is a lot of misunderstanding how RAM and swap files work and...

forums.macrumors.com

 

[throAU]

Recently I read that ram is shared between the CPU and GPU on M1 processors. Does this mean that some of my ram will be allocated to driving an external display? Wouldn’t the GPU have its own dedicated vram so that it wouldn’t cut into ram allotted to the cpu?

Yes the RAM is shared.

This is by design, because the RAM is shared, there's no need to copy data out of CPU RAM into GPU RAM, saving both a lot of power and improving performance. Also it means the GPU can access up to 64GB as GPU memory.

If you're worried about this, go large on memory - 32 GB or 64 GB.

and yeah, driving an external monitor is no problem. I've got a 4k display attached right now and can't notice any real difference with it connected vs. not.

 

[Erasmus]

The amount of RAM that the GPU would need to allocate to itself (dynamically of course) to drive the internal or even multiple external monitors is negligible. The RAM is properly shared between CPU and GPU, so it's not like normal iGPUs where a large slab is reserved for the GPU. Actually, considering the GPU can see everything in RAM and the CPU can see everything in the 'VRAM' (because they are the same thing here), you shouldn't end up with the duplication of data that other computer architectures would generally have.

If you need 32GB of main system RAM, you shouldn't need to worry about getting extra specifically because of the GPU. Unless you also specifically need large amounts of VRAM simultaneously with system RAM, for example if you were planning on doing heavy GPU processing AND CPU processing in different applications simultaneously.

In terms of actual sizes, I think you might be looking at dozens, maybe hundreds of MB used by the GPU for your frame buffer if you're just using the GPU for standard display UI stuff.

 

[yitwail]

I'm not an expert on GPU by any means, but GPUs do a lot more besides drive external displays, such as 3d graphics computation and video encoding & decoding. So, the amount of memory it would use depends on the task, as well as the resolution of the external monitor. Playing an AAA game at high frame rate requires much more 'unified memory' than watching video, for example.

 

[davedirect]

I really appreciate all of the responses and information. Thank you. I need the 32gb of ram for running sample libraries in Logic Pro and Ableton, and I am definitely not ever going to do any GPU intensive work at all. In my case, it sounds like the amount of ram used in my case will be negligible, even if I’m running an external 4K screen. The most I’ll be needing it to handle is standard UI stuff on both the built in and external display.

By the way, does running an external monitor use a significant portion of the CPU or is it pretty negligible? Again, I would just be doing music production on the built in and external monitor, (same project.)

 

[Erasmus]

Running an external monitor on any modern computer (or really anything in the last decade) should have a negligible effect on resources.

What you intend to do with that extra screen (extra apps running, etc) may change that though.

In your case, it doesn't seem like even running 3-4 extra monitors would have any noticeable effect on the computer.


EDIT: New-ish Intel laptops WITH DISCRETE GRAPHICS CHIPS often do have massively higher power draws and temperatures when an external monitor is plugged in, but this is not affecting RAM usage. That is because normally the integrated (on CPU die) GPU powers the internal monitor, but plugging in an external monitor forces the computer to switch to discrete GPU. That is a system design issue. Intel Macs without discrete graphics (e.g. 13" MBP) don't have this issue, as they just run the external monitor using the iGPU, using almost no extra power.

Apple Silicon doesn't have this issue either, as the vastly more efficient and more powerful integrated GPU is wired to run both the internal and external screens.

I believe the 16" Intel MBPs were further bugged in that they weren't just switching to the discrete GPU with an external monitor, but also seemed to have it running at high power, even when it wasn't doing anything.

 

[davedirect]

Running an external monitor on any modern computer (or really anything in the last decade) should have a negligible effect on resources.

What you intend to do with that extra screen (extra apps running, etc) may change that though.

In your case, it doesn't seem like even running 3-4 extra monitors would have any noticeable effect on the computer.

Right on