A total of seven architectures are officially supported for "trixie":
"trixie"
64-bit PC (amd64),
64-bit ARM (arm64),
ARM EABI (armel),
ARMv7 (EABI hard-float ABI, armhf),
64-bit little-endian PowerPC (ppc64el),
64-bit little-endian RISC-V (riscv64),
IBM System z (s390x)
It's good to see RISC-V becoming a first-class citizen, despite the general lack of hardware using it at the moment.
I do wonder, where are PowerPC and IBM System z being used these days? Are there modern Linux systems being deployed with something other than amd64, arm64, and (soon?) riscv64?
Mainframes are still holding on in use cases where a single server having continuous uptime is vital. They're designed to have uptime measured in decades, so even components like the processors and main memory have hot spares available and can be hot-swapped without interrupting the OS or running services. They also have continually running system monitoring and diagnostics at the hardware level (not running as an OS service) that will alert both the owner and IBM if they detect some sort of hardware fault. IBM has supported Linux as a first-class OS option for their mainframes since the early 2000s.
From a developer perspective, s390x is also the last active big-endian architecture (I guess there's SPARC as well, but that's on life support and Oracle doesn't care about anyone running anything but Solaris on it), so it's useful for picking up endianness bugs.
Another interesting thing is that the only two 32-bit architectures left supported are armel and armhf. Debian has already announced that this will be the last release that supports armel (https://www.debian.org/releases/trixie/release-notes/issues....), so I guess it'll be a matter of time before they drop 32-bit support altogether.
Yeah, mainframes are all about cases where the uptime is critical. Most modern systems are good with offering 99.9% or 99.99% reliability, with the understanding that trying to offer more than that just gets more and more expensive. Well... spending huge amounts of money on mainframes is one of the strategies to get to reliability numbers like 99.9999999%.
The legitimate usage is typically for workloads like relational databases (which are anyway single-machine architectures) that experience heavy load 24/7, part of fragile architectures that cannot tolerate downtime (remaining fragile as such because the original source code has been lost etc.), where "the system is down" causes tens of thousands if not hundreds of thousands of people to stop work.
Both Power and z are many billion dollar businesses each. Banking and other high finance is the stronghold for both. IBM still seems proud of z, Power seems merely tolerated these days which is a shame because it is a nice ISA and the systems are very nice too.
I do wonder, where are PowerPC and IBM System z being used these days? Are there modern Linux systems being deployed with something other than amd64, arm64, and (soon?) riscv64?