Thread by @ErrataRob

By the way, it's worth pointing out that ARM server market share is still less than 0.1%.

Everybody knows it'd be better to build servers from power-efficient ARM chips than hungry Intel chips.

Everybody is wrong. It's a good example of how everybody can be wrong about a thing.

The trade press has been full of stories promising that "ARM servers", based on the same power efficient chips in our mobile phones, are just around the corner. Big companies like Facebook, HP, Amazon, Google, etc. have made big investments here.
wired.com/2013/05/hp-arm…

And yet, here we are years later, and no such servers have materialized. Why is that? There are two basic answers. The first is that ARM chips aren't more power efficient. The second is there's no commodity devices.

ARM chips use less power, true. But that's simply because they are slower. Computations-per-watt is roughly the same, even slightly worse. If you scale up ARM chips to the same computation power as Intel server chips, they consume as much power or more.

Also, how you "scale" speed is meaningful. Instead of one chip at 4GHz you might instead have two smaller chips at 2GHz each. Such scaling works in some cases when things are easily parallel, but most workloads have big sequential bits where that 4GHz really helps.

In addition, all the additional circuitry coordinating and communicating between two 2GHz cores adds up to more power consumption.

Early "ARM server" designs focused on this many core idea, and chips doing this shipped, which nobody bought. For this reason, ARM has focused the last several years on creating big core designs that get close to Intel's single-core performance, maybe not 4GHz, but close.

These designs won't ever have a power efficiency advantage. But they don't have to in order to compete. ARM doesn't build chips, only designs. Its partners build the chips, a wide variety with different capabilities, with added silicon for things like crypto acceleration or AI/ML

The other reason ARM servers fail to compete with Intel is commodity pricing. My laptop uses essentially the same hardware as a high-end server. I can develop and test on my laptop, and then copy it up to a server in the cloud.

I can't do the same with ARM hardware. Maybe there is a server hardware with some key advantage, such as video transcoding for my teleconferencing app. The development process for that hardware is extremely expensive and difficult.

Key developers that can work in such environment are hard to come by. It's much easier to develop for commodity Intel hardware and rent more servers.

This is especially true as technology evolves. Two years from now, Intel CPUs will have surpassed those custom chips in video transcoding. It won't be another 5 years before that custom chip will be updated. And then, it'll be completely different requiring new development.

So while you'll get temporary design wins for ARM specialty chips, significant penetration of Intel's server market will be out of reach -- form this direction.

But if "commodity" is the issue, then maybe ARM will win from the other direction. Instead of high-margin/high-end servers, maybe it'll come from Raspberry Pi class devices. Tens of millions of these devices have been sold for $35 each.

There are many Raspberry Pi competitors, basing their products on different variations of ARM processors. There are also other ARM-based devices, like home routers or Android TV settop boxes, that can be repurposed as servers.

The latest Raspberry Pi 4 has a dramatically faster chip than the older version. It's more power hungry than equivalent Intel chips, but at the same time, is powerful enough for "server" applications.

It's powerful enough you can actually use it as a desktop, just add a monitor, keyboard, and mouse. I run and test all my code on my little RPi4. It's commodity hardware that opens the doorway for developers to develop on.

As far as I can tell, the RPi4 is the only ARM device that runs Linux. By "Linux" I mean any Linux really, Ubuntu, Debian, RedHat, with old kernel versions or the latest. All other ARM devices are limited to what Linux they'll run, often with outdated kernels.

There are lots of RPi competitors, but they all struggle with supporting only the Linux kernel that was current when the chip was shipped, and never updated after that point.