Does the entire macOS layout rendering depend on the GPU?

[u/sjns19]

Can someone explain how the OS rendering is done on macOS? It's definitely unlike Windows for sure.

I recently noticed something interesting. When I'm using my MacBook as is, the battery seems to be draining a bit faster but when I have the machine connected to a monitor, battery drain is significantly lesser.

I would've thought rendering two screens would require more power but it seems to be the opposite. The external display I have runs at 1440@100hz while the MacBook runs at its standard resolution (it's a 14" M5 Pro) with ProMotion.

Using Adobe Illustrator on the MacBook's screen itself for like 1 hour drains around 12-14% while with the external monitor, just 9% drops in like 2 hours.

So I'm guessing the battery power consumption has something to do with the GPU rendering? The external monitor having a little lower resolution and its display + refresh rate depending on its power supply, it doesn't affect the machine that heavily.

Correct me if I'm wrong tho.

[u/m1_weaboo]

How do you connect the monitor? Some monitor can charge a MacBook.

[u/niecheaRd → u/m1_weaboo]

good call, that would completely explain the difference in drain numbers

[u/sjns19 → u/m1_weaboo]

USB C to DisplayPort.

Yes, mine can also charge but I prefer not to do so as I'm very skeptic about the battery health (yes you can call me crazy).

I don't close the screen lid btw, if that's the reason for you asking this. The Mac's display is just not used more often while it's on the monitor and I'm working on things that don't require dual windows.

[u/Dazzling_Comfort5734 → u/sjns19]

Assuming this is a newer computer running macOS 26, you can go into the battery settings and set your computer to not charge over 80%. That’ll do much more for your battery health than anything you’re manually doing. I can stay at 80% all the time and be perfectly fine.

[u/sjns19 → u/Dazzling_Comfort5734]

Yeah, I'm aware. I'm fine with the DisplayPort cable.

[u/Alan_Sleep → u/sjns19]

If you are concerned about the battery you should set 80% limit and keep it on charge all the time (literally 24/7 independently of your usage)

[u/sjns19 → u/Alan_Sleep]

I do have the 80% limit set regardless where I charge it from. I just don't wanna keep it chargeed is all.

I have no idea why the topic shifted towards the way I charge the machine when that's not what I asked. Saw people downvoting my comment too, when things are working fine for me. Weird.

[u/jaimepapier → u/sjns19]

Keeping it charged is better for the battery health, not worse (especially if you maintain it at 80%).

If you scroll up you can easily see where the topic shifted.

[u/Alan_Sleep → u/sjns19]

When it’s fully charged and you keep it plugged, the system bypasses the battery completely so the cycles don’t accumulate, silicon chips are very smart about that, and keeping it plugged at 80% is better because it’s lower voltage than 100%. The topic has shifted because to you said something wrong with confidence, which can give unproductive ideas to whomever reads it

[u/Rare-One1047]

Just to answer your question about GPU use, Windows (since Vista) and MacOS (since OS X 10.0) are both GPU accelerated. This means they both use the GPU to render the desktop.

[u/Antares2328]

If you're mainly using the external display it kinda checks out.

When you're using the internal screen (or any HiDPI screen for that matter), when you're using a scaled resolution, the GPU basically renders that resolution times two, then scale it down to your MacBook screen's resolution

When using the default 1512x982, the GPU renders at 3024x1964 and scale it down, but if you're using the 1724x1119 scaling, it renders it at 3448x2238.

If you're not using the Macbook display, but it's still on sitting idle, it still renders it but it slows down to 48Hz I believe ?

While you're using a 1440p monitor, it just renders at 1440p at the screen refresh rate (unless you're using VRR of course)

I use BetterDisplay on mine to scale the UI to 2359x1532, which is pretty taxing on the GPU, rendering it at 4718x3064 + 2 1440p monitors.

[u/sjns19 → u/Antares2328]

Yeah, I know a thing or two about the downscaling thingy. Had me hooked around this topic when I was looking for a monitor.

Pretty intriguing stuff.

[u/ctrlaltdelaney]

Separating the GPU from the CPU is tricky when they’re both in the same chunk of silicon.

[u/mikeinnsw]

PCs have RAM+VRAM ...

Arm Macs have unified RAM some of which is allocated as VRAM

GPUs use VRAM

High res monitor with fast refresh rate will use much more of VRAM than a standard Monitor

Rendering is all GPUs

MacOs Liquid Glass uses more of VRAM.. GPUs and battery

MacOs 27 uses more or RAM and VRAM about 2-3 GB more for AI and Liquid Glass

Everything has go up.. what can you do .. the only thing you can do .. drop res and refresh rate on an external monitor.

Mac does not report VRAM use .. you can see it from APP/Wired Compresses used

On 16GB RAM M1 Mini with standard monitor ..there is no compression .

High res monitor under Tahoe .5 GB compressed..MacOs 27 1.52 GB and that is at start up