Memory Bandwidth in Apple’s M1

The memory bandwidth on the new Macs is impressive. Benchmarks peg it at around 60GB/sec–about 3x faster than a 16” MBP. Since the M1 CPU only has 16GB of RAM, it can replace the entire contents of RAM 4 times every second. Think about that…

Some say we’re moving into a phase where we don’t need as much RAM, simply because as SSDs get faster there is less of a bottleneck for swap. Indeed, SSDs have made significant strides, especially with the newest Samsung 980 NVMe drives pushing 5-7GB/sec. This is closer to the memory bandwidth than we’ve ever been with consumer-grade hardware, and you’re only running about a third of the speed of main memory in a 16” MBP. However, with the huge jump in performance on the M1, the SSD is back to being an order of magnitude slower than main memory.

So we’re left with the question: will SSD performance increase faster than memory bandwidth? And at what point does the SSD to RAM speed ratio become irrelevant?

Theoretically, SSD swap is “fast enough” if it can load data from a backgrounded app into main memory before the user notices a delay when clicking an icon in their Dock. Once this threshold is reached, there’s not much of a distinction between an app being open or not.

I do believe that a limited amount of RAM is becoming less of an issue as time goes on. As I’m writing this, I’m 5GB into swap on my 16” MacBook Pro with 32GB of memory. In years past, a Mac 5GB into swap would have felt like it was crawling. However, today I haven’t noticed a single hiccup, and honestly wouldn’t even be aware of the swap usage if XRG wasn’t sitting on my desktop telling me so.

Would I buy a Mac with 16GB of RAM to use as a primary development machine today? No, probably not. While I don’t typically notice a speed decrease due to swap usage, I don’t think that storage threshold has been reached quite yet. However, I’m looking forward to Apple’s answer to the higher-end market and am confident they have M-series chips with more RAM in the pipeline.