# <a id="cpu"></a>CPU Limitations

This limitation comes in two subclasses:


## <a id="emu"></a>There Is No Built-In CPU Emulation

Docker lets you run an image built for another architecture on your local system through transparent CPU emulation. If you are on an x86_64 host, this command should drop you into an Alpine shell:
Docker lets you run an image built for another architecture on your local system through transparent CPU emulation. If you are on an x86_64 host, try this command:

    $ docker run --rm -it --platform linux/arm64 alpine:latest
    $ docker run --rm -it --platform linux/arm/v7 alpine:latest uname -m

That should yield “`armv7l`”, an entirely different CPU architecture from your host. Even if you try this on an ARM64 host (e.g. an Apple Silicon macOS box) you have a different word size here.

The same will work on recent versions of Podman, and you can get it to work on old versions of Podman with a bit of manual setup.(^It’s off-topic to go into the details here, but it amounts to “`podman machine ssh`” followed by a “`dnf install qemu-static-*`” command.)
You will get the same result on recent versions of Podman, and you can get it to work on old versions of Podman with a bit of manual setup.(^It’s off-topic to go into the details here, but it amounts to “`podman machine ssh`” followed by a “`dnf install qemu-static-*`” command.)

For that to work under `container.npk`, the RouterOS developers would have to ship the QEMU and Linux kernel [`binfmt_misc`](https://en.wikipedia.org/wiki/Binfmt_misc) bridges needed to get the OS to accept these “foreign” binaries. Since it would approximately double the size of RouterOS to do this for all the popular CPU architectures, they naturally chose _not_ to do this.
For that to work under `container.npk`, the RouterOS developers would have to do the thing Docker and Podman do: ship the QEMU and Linux kernel [`binfmt_misc`](https://en.wikipedia.org/wiki/Binfmt_misc) bridges needed to get the OS to accept these “foreign” binaries. Since it would approximately double the size of RouterOS to do this for all the popular CPU architectures, they naturally chose _not_ to do this.

What this means in practice is that you have to be sure the images you want to use were built for the CPU type in your RouterOS device. This is true even between closely-related platforms. An ARM64 router won’t run a 32-bit ARMv7 image, if only because it will assume a 32-bit Linux kernel syscall interface.
What this means in practice is that you have to be sure the images you want to use were built for the CPU type in your RouterOS device.

<a id="qemu"></a>There is an exception: you can ship your own CPU emulation. Take [this thread](https://forum.mikrotik.com/viewtopic.php?t=189485), for example, which describes a container that bundles the 32-bit Intel-compiled `netinstall-cli` Linux binary along with an ARM build of of `qemu-i386` so that it will run on ARM RouterOS boxes. For a process that isn’t CPU-bound — and NetInstall is very much I/O-bound — this can be a reasonable solution as long as you’re willing to pay the ~4 megs the emulator takes up.
<a id="qemu"></a>There is a path around this obstacle: ship your own CPU emulation, as was done in [this forum thread](https://forum.mikrotik.com/viewtopic.php?t=189485), which describes a container that bundles the 32-bit Intel-compiled `netinstall-cli` Linux binary along with an ARM build of of `qemu-i386` so that it will run on ARM RouterOS boxes. For a process that isn’t CPU-bound — and NetInstall is very much I/O-bound — this can be a reasonable solution as long as you’re willing to pay the ~4 megs the emulator takes up.


## <a id="compat"></a>It Only Supports Intel and ARM

MikroTik has shipped an awful lot of MIPS-based product over the years, and it continues to do so, most recently as of this writing in their [CRS518-16XS-2XQ-RM](https://mikrotik.com/product/crs518_16xs_2xq). Atop that, there are other CPU architectures in the historical mix like PowerPC and TILE. MikroTik doesn’t ship a `container.npk` for any of these platforms.

But why not?