alt Hacker NewsThe issue was not that Alpha ISA was impossible to scale down.
The issue was that DEC lacked the resources to run a completely new microarchitecture design to target low-power platforms, and the failure was trying to push an extreme performance chip into low-power envelope instead of designing a new one.
AFAIK with ARM the difference is that they started with low-power underpowered chip and modified it to bring the performance up.
You'd have probably similar issues trying to make a phone using Fujitsu A64FX (the supercomputer ARM) into low-power chip.
This interview with Allen Baum seems to imply that DEC was quite aware of what could easily be done with Alpha, and what could not.
I'm also assuming that ARM code density was better than Alpha (conditional opcodes being a major contributor).
"Well, we were looking at doing a low power Alpha and decided that just couldn’t be done, and then looked at the ARM. We think we can make an ARM which is really low power, really high performance, really tiny, and cheap, and we can do it in a year...
"Well, I worked on the StrongARM 1500, which was a very interesting product. It was an ARM and a DSP kind of highly combined... And then we finished that project and our group in Palo Alto, we were just gonna start an Alpha project."
https://archive.computerhistory.org/resources/access/text/20...