Rpi considerations

QEMU is not purely a collection of software emulators, although it does contain those.

QEMU is the frontend, ie the thing that implements all the various I/O devices and options like video drivers, virtual networking, USB passthrough, all that stuff.

QEMU supports a number of virtualisation backends. These just take care of virtualising CPU instructions and providing the memory model - accesses to I/O are trapped and passed through to QEMU to emulate. There are three popular ones:

1. KVM is Linux's virtualistion backend, which only works if host architecture == guest architecture
2. Apple's virtualisation and hypervisor frameworks do a similar thing on Macs
3. QEMU contains its own cross-architecture emulation backend called TCG. If you want to run one arch on another it's probably using TCG.

If you're running KVM on Linux then you're likely to be running QEMU in the frontend to implement your I/O and interface with the world. Orchestration tools like virt-manager and libvirt mean you may not be touching QEMU directly, but there is a QEMU running further down the stack. ie KVM almost certainly implies QEMU but QEMU doesn't imply KVM.

(QEMU also does user-mode emulation, using TCG to run individual Linux binaries of one arch on another. That's something else entirely)

Theo

Oh, that's super useful:

Short-idle mode means a state where the computer has reached an idle condition five minutes after operating system boot, after completing an active workload, or after resuming from computer sleep mode, and the primary computer display is on and the computer remains in the working mode ACPI G0 (S0)

Long-idle mode means a state where the computer has reached an idle condition 15 minutes after operating system boot, after completing an active workload, or after resuming from computer sleep mode, and the primary computer display has entered a low-power state where screen contents cannot be observed (for example, backlight has been turned off) but remains in the working mode ACPI G0.

Yes, exactly what I was hoping for.

Thanks, that saved me a job too.

Correct, but you have to look hard to find that information before buying.

My always-on machine which does mail server / monitoring / mqtt and lots of other light stuff together with a desktop for when I don't need the big machine is an Intel NUC D34010 - 16GB RAM, SATA SSD, uses about 5W when sitting idle at the desktop (measured).

I configured fancontrol so that the fan is stopped as long as the CPU is below 60°C (which is normally is).

The i3 is fast enough for normal use (I use debian with XFCE). I have a Pi

cu Michael

And you are also behind times - the west is gone - long live Alibaba/AliExpres (joking).

I bought Acresser devices in 2007/2008 right before the financial melt down. They cost 250 US and were kind of picky to set up. Last year one of them died (well the ide-to-CF controller gave up). The cool thing about those were that they used max.12W. I started looking everywhere (in the west). I couldn't find anything useful. Min. power consumption >60W and costs >600,- ... and then I went to Alibaba/AliExpres ... it felt like I found a treasury. BTW the NUC and the kind of are not bad - but non had more than one LAN port

• power consumption + price. It is a disappointment what happened after 2008 ... but not going into politics and economics. Just have a look at Alibaba/AliExpres.

I paid 100€ for the D34010. Yes, if you need more than 1 lan port you need to look elsewhere (in some use cases, a USB3 ethernet adapter might work).

There are current (Intel gen-12 and newer) machines that are in the ~5W idle ballpark, but these tend to cost a lot more.

I regularly buy chips and breakout boards there. Getting reliable information about power consumption before you buy is a big problem, and warranty/back-shipment costs is another.

Also, I am quite wary of chinese equipment using mains voltage.

I just bought a JBC-compatible soldering station from aliexpress. It works fine, but electrical safety is less than marginal: less than 1mm creepage distance from mains to the non-grounded metal case is definitely not OK.

I had to build a new housing (and used a different, safe power supply). In this case it was worth the effort and I had considered this before buying, but for a mini-PC, I would rather buy something that can be used out of the box without danger of electrocution.

cu Michael

Ah but will they last so long? A SBC at half the price costs you more if you have to buy three replacements over the lifespan of the expensive one. Then there's the many hours wasted working around the failure and re-ordering, after which you'll be inclined to buy a second one as a spare anyway.

Many years ago I experimented with buying computer-related devices off AliExpress and Chinese Ebay sellers. Most failed much sooner than I expect from such gear, if they worked at all. When looking for a saving now my preference has turned to buying second-hand models from a good brand off Ebay or similar websites. Even used devices have proven more reliable than AliExpress standard stuff, plus the used sellers aren't so busy trying to trick you into thinking you're buying something you're not (and sometimes not sending your order if you pick a good deal that they listed by accident!) like on AliExpress. Often it's actually cheaper too, if you have the patience to wait for the right listing to come along.

For things without electronics in them like cables and connectors, I use AliExpress a lot though. I just don't trust them with a transistor. Though I did buy some allegedly (and authentic looking) second-hand known-brand RAM from China on Ebay and that has lasted well.

Yeah I ruled out the NUCs on power consumption, but now I see from the mentioned spreadsheet that the idle power can be far below the PSU specs, they're back as an option.