[mcbridematt]

Ah, that explains this patchset that was submitted to the Linux kernel today

"KVM: s390: Introduce arm64 KVM"

"By introducing a novel virtualization acceleration for the ARM architecture on s390 architecture, we aim to expand the platform's software ecosystem. This initial patch series lays the groundwork by enabling KVM-accelerated ARM CPU virtualization on s390....."

https://patchwork.kernel.org/project/linux-arm-kernel/cover/...

[trebligdivad]

Oh that's a weird way to do it; they used to have an x86 add on block for mainframes which was just a pile of x86 blades with some integration.

[bombcar]

I loved the era of "daughter cards" which were just entire computers on a board.

things like https://www.youtube.com/watch?v=a6b4lYOI0GQ could get you a really interesting form of multitasking

[mikepurvis]

From the perspective of PC building, I've always thought it would be neat if the CPU/storage/RAM could go on a card with a PCIe edge connector, and then that could be plugged into a "motherboard" that's basically just a PCIe multiplexer out to however many peripheral cards you have.

Maybe it's gimmicky, but I feel like you could get some interesting form factors with the CPU and GPU cards sitting back-to-back or side-by-side, and there would be more flexibility for how to make space for a large air cooler, or take it up again if you've got an AIO.

I know some of this already happens with SFF builds that use a Mini-ITX motherboard + ribbon cable to the GPU, but it's always been a little awkward with Mini-ITX being a 170mm square, and high end GPUs being only 137mm wide but up to 300mm in length.

[yjftsjthsd-h]

Oh, going back to a backplane computer design? That could be cool, though I assumed we moved away from that model for electrical/signaling reasons? If we could make it work, it would be really cool to have a system that let you put in arbitrary processors, eg. a box with 1 GPU and 2 CPU cards plugged in

[mikepurvis]

I believe PCIe is a leader/follower system, so there'd probably be some issues with that unless the CPUs specifically knew they were sharing, or there was a way for the non-leader units to know they they shouldn't try to control the bus.

[bombcar]

But if we're dreaming, we can have the backplane be actually multiple (Nx thunderbird 5 cables connected each slot to all other slots directly).

Then each device can be a host, a client, at the same time and at full bandwidth.

[SoftTalker]

That's basically what S-100 systems were, isn't it (on a much slower bus)?

[tssva]

There were also PC compatible systems based around ISA backplanes. This was especially common for industrial computers but Zenith/Heathkit made ISA backplane based systems for the business and consumer markets. I own a Zenith Z-160 luggable computer from 1984 which uses an 8 slot 8-bit ISA backplane. 1 slot is occupied by a CPU card which also has the keyboard connector. My system has 2 memory cards which each provide up to 320k along with a serial and parallel port. Zenith sold a desktop version of this as the Z-150. They later released models based upon 16-bit ISA backplanes. I think but am not sure of the top of my head that the last CPU they produced a 16-bit card for was the 486.

[BirAdam]

Yes, but also in many other scenarios. The last backplane systems I saw were 90s industrial 486s.

[bombcar]

This was (is?) done - some strange industrial computers for sure and I think others, where the "motherboard" was just the first board on the backplane.

The transputer b008 series was also somewhat similar.

[throwup238]

That would crush latency on RAM.

[mikepurvis]

The RAM and CPU would still be on the same card together, and for the typical case of a single GPU it would just be 16x lanes direct from one to the other.

For cases where there are other cards, yes there would more contention, but few expansion cards are able to saturate more than a lane or two. One lane of PCIe Gen5 is a whopping 4 GB/s in each direction, so that theoretically handles a dual 10gige NIC on its own.

[Teever]

That's what I was hoping Apple was going to do with a refreshed Mac Pro.

I had envisoned a smaller tower design that with PCI slots and Apple developing and selling daughter cards that were basically just a redesigned macbook pro PCB but with a PCI-E edge connector and power connector.

The way I see it a user could start with a reasonably powerful base machine and then upgrade it over time and mix and match different daughter cards. A ten year old desktop is fine as a day to day driver, it just needs some fancy NPU to do fancy AI stuff.

This kind of architecture seems to make sense to me in an age where computers have such a longer usable lifespan and where so many features are integrated into the motherboard.

[raw_anon_1111]

You can do basically that by connecting over Thunderbolt 5

https://news.ycombinator.com/item?id=46248644

[bigyabai]

Homogenous RDMA is less like a daughterboard and more like a brother or sisterboard.

[bombcar]

M5 processor plugged into the same RDMA as IBM POWER for that "brother from anothermotherboard".

[Grosvenor]

Apple already experimented with this with the prototype Jonathan computer. It's very late 80's in its aesthetic, and I love it.

https://512pixels.net/2024/03/apple-jonathan-modular-concept...

[bombcar]

This is the kind of glorious thing that will only appear when Moore's law is dead and buried.

[wat10000]

Now we have cables that include computers more powerful than an old mainframe. So if it pleases you, just think of all the tiny little daughter computers hooked up to your machine now.

[bitwize]

Or even Doom on your Beeb: https://m.youtube.com/watch?v=32hJLwrk-gY

[rbanffy]

Z/OS for ARM then? ;-)

I’ve been running VM/370 and MVS on my RPi cluster for a long time now.

[kraftverk_]

Cool, can you share more about the setup?

[rbanffy]

A 4x RPi Zero Ws Docker Swarm cluster running the dockerised versions of Hercules with VM/370 Sixpack, VM/370 CE and MVS TK 4. All in an IKEA picture frame.

[raverbashing]

But I wonder if this is "much better" than x86 emulation or virt?

Is there really SW that's limited to (Linux) ARM and not x86?

[Jarwain]

Technically aren't most android apps limited to ARM?

[toast0]

There's certainly some, but I don't think most.

I'd guess most apps are bytecode only, which will run on any platform. Some apps with native code have bytecode fallbacks. Many apps with native code include multiple support for multiple architectures; the app developer will pick what they think is relevant for their users, but mips and x86 are options. There were production x86 androids for a few years, some of those might still be in user bases; mips got taken out of the Native Development Kit in 2018 so probably not very relevant anymore.

[wmf]

Probably Intel and AMD aren't willing to do this deal but Arm is.

[kev009]

IBM actually owns x86 rights still. They last used it to do something similar called Lx86 which ran x86 VMs on POWER CPUs.

[wmf]

Developing a good x86 CPU is far beyond IBM's abilities. The rights aren't enough.

[kev009]

Price competitive to AMD and intel? Sure. Abilities? There is no magic, the Tellium and Power11 are each as complicated as something like Epyc and the former has both a longer and taller compatibility totem pole than x86.

Anyway this post was never about building ARM or x86 CPUs, the point is they could have done a zArch fast path for x86 for "free", so there is some other strategy at play to consider doing it with ARM.

[MikePlacid]

> Is there really SW that's limited to (Linux) ARM and not x86?

MacOS? (hides)