> Not only faster, but I bet simultaneously accessible from both the CPU and GPU.

It is. We know they're using a unified memory architecture, they pointed it out in the presentation.

Unified doesn't necessarily mean dual ported.

Due to how DRAM works the array itself cannot have more than one port and almost certainly even the DRAM chip as a whole is still some variation of single ported SDRAM (long time ago there were various pseudo-dual-ported DRAM chips, but these were only really useful for framebuffer-like applications). But given that there are multiple levels of cache in the SoC it is somewhat moot point.

LPDDR4x (the ram chips in the m1) comes in dual port flavors.

I suspect you mean they come with two channels on a single chip, which is not the same as two ports. Channels access separate bits of memory. Ports access the same bits of memory.

Nope. Nothing too magical, I suspect. It says LPDDR4 right there in System Profiler, although it does not indicate the frequency.

This reminds me that Xbox series X/PS5 use Unified GDDR for higher memory bandwidth, I'm curious if such design can help x86 catch up M1?

x86 has been doing unified memory for integrated GPUs since at least 2015. It's not a new thing, see for example https://bit-tech.net/news/tech/cpus/amd-huma-heterogeneous-u...

The reason GDDR isn't typically used for system RAM is it's higher latency & more power hungry. Like, the GDDR6 memory on a typical discreet card uses more power than the an entire M1-powered Mac Mini power hungry.

Thanks, I haven't noticed the latency/power difference of GDDR memory.

no its normal mobile ram

The M1 has 4 LPDDR4x chips inside the the CPU package running at 4266 Mhz and showing some of the best latencies I've seen.

What "normal" laptop has that?

I believe the poster meant "normal" in the sense that it's a conventional memory technology for laptops. (ie LPDDR4 not GDDR like had been suggested above).

being inside the cpu package should allow for less than a 1% improvement in latency by my napkin math. its got good latency because it is a top of the line mobile ram setup but that isn’t unique to m1

I 100% agree, but I've audited my code, and on other platforms my code closely agrees with LMbench's lat_mem_rd, which seems pretty well regarded for accuracy.

The latency appears real to me.