John Siracusa

They were optimized for moving huge amounts of data into and out of the GPU.

And how did that data get into VRAM?

Well, the computer would ship it over, probably out of its regular RAM, and it would say, here, video card, you're going to need these textures and this geometry to do your work.

It would send it over the bus, PCI bus or whatever, AGP bus, whatever bus was the bus of the day, and it would go into VRAM, and the GPU would read and write to VRAM and do all of its stuff.

So you had these two pools of memory, regular RAM that the CPU used, and then VRAM that the GPU used.

Unified memory means not having a separate pool of VRAM and regular RAM.

Macs and the Apple Silicon age have one pool of RAM that is used by the GPU as it's quote unquote VRAM and by the CPU as it's regular memory.

And it's any part of the RAM can be used by either one.

And they both have a really fast, really high bandwidth connection to that RAM.

That's how it works, right?

If it was just like, you know, just have a GPU and a CPU and just one pool of RAM, that one pool of RAM would be too slow and too low bandwidth.

That's why they had VRAM, special VRAM with really high bandwidth to the GPU.

But what Apple did is they said, we're going to take our RAM and we're going to make it a huge, wide, fast, low latency bus and solder the chips right next to the SoC.

And now that pool of memory can be used by both.

And this is one of the reasons why the early days of people saying like,

oh, it's okay for a Mac, Apple Silicon Mac to have a smaller amount of RAM because it has unified memory and that makes it use less RAM.

The opposite is true.

Back in the day, if you had like, you know, one gigabyte of regular RAM and 512 megabytes of VRAM, you had a total of 1.5 gigabytes of RAM in that machine.

500 gigs for the video card and one or 500 megs of video card and one gig for the ram right if you unified that you'd want it to be combined you say okay well i'm just going to throw away the vram and leaving you with just the one gig now you have less ram so it seems like you have less memory it's like now i have the the gpu fighting with the cpu for who's going to get to use what part of the one single pool of ram and in apple's case that one single pool of ram isn't any bigger and

So yeah, it seems like you're wasting more memory unless you always have the same amount you have.