This hobby project has added quite a bit of features and I think the architecture will be interesting to the OS aficionados on this forum. See

https://www.youtube.com/watch?v=_DG_4CkjV9I

The most interesting thing perhaps is that I was able to isolate the x86 core stuff into arch-metal lib that implements arch-abi trait. The way it's setup is such, that I also implemented the trait by wrapping QEMU TCG engine (unicorn) and also a full kvm variant. The actual kernel (vfs, dos personality, linux personality, threading, ...) is written in almost entirely safe rust calling into a handful of arch functions through the arch-abi trait. This means that the same kernel can be build in three modes,

1) metal. It's a full OS with both legacy bios and modern uefi compatibility. So it can run on old machines with vga compatible graphics and sound blaster and it will expose this. But it can also run on uefi with hda, in which case vga and sound blaster is emulated, so you can still play your retro-games directly on the machine.

2) interpreted. This is basically dosbox mode, the QEMU TCG emulates the userspace programs, while the kernel is compiled as a regular app running native on the host machine. This can be played on any architecture.

3) kvm. This is basically dosemu2 mode. The userspace apps run natively on the cpu under kvm hypervisor, the kernel still runs as a regular app on the host machine. Most of the hosted specific code is shared with interpreted mode. The only differnce is that TCG is replaced with native execution using kvm

All the three modes above run the exact same kernel, with only a different implementation of the arch-abi injected. This actually is quite convenient as one can just run and debug the kernel like any normal app. No need to hook gdb through qemu or that kind of tricks.

So far it allows me to play my favorite games from my youth again on my razer laptop which is very satisfying. You can use it by just copying the kernel into your ext4 /boot directory, setup grub entry and /home/retroos becomes c: . You have access to your linux tools by starting shell.elf in c:\boot , but this is still work in progress (ls/cat/echo work but I'm not close to full linux environment). Of course I recommend qemu and installing it on your computer as in the video above is at your own risk. Anyway the project is complete enough that it might appeal to some retro hobbyist.

Of course I used AI as a "compiler" to compile DOS syscall spec to rust, compile the DPMI spec to rust, linux syscall API to rust. But the design and architecture is mine and you can see that that is still very similar to my code written back in 2023 in this repo. The design of the OS seems to occupy a somewhat new/original spot in the OS design space, sharing features and ideas with many other concepts in kernel design but in a unique way.

It is a monolithic kernel, one elf linked together, but it shares many ideas with microkernels. Arch is a microkernel , but uses just function calls instead of messages. The arch design is more like a hypervisor then the standard osdev tutorial/linux flow, which allows to abstract the core as a library. I haven't seen the trait factorization, ie. providing different ways of running the same kernel, done this way, but it of course strongly reminds one of UM-linux.

What I certainly havent seen before is using recursive paging in a way that unifies 32bit PAE paging and x64 paging, allowing the kernel to seamlessly toggle between 32bit and 64bit mode, which allows vm86 and 64-bit code to execute under one kernel (without the virtualization instruction set).

Specs:
It should run on 386/bios all the way up to x64/uefi without CSM. If you have an old computer with an actual sound blaster, games can use it natively. Otherwise sound blaster/adlib (experimental gus) is supported over hda/ac97 systems. Also when vga is not available, vga is emulated over the regular framebuffer. The video is RetroOS running on a razer (2025) with realtek hda. Old 486/sb I only tested through qemu/bochs/86box emulators.

Hi, @gsos,
This is one very interesting project. Maybe I'm wrong, but at first glance it looks to me like a DOS (compatible) kernel without COMMAND.COM support.

aVd wrote on Today, 07:45:

Hi, @gsos,
This is one very interesting project. Maybe I'm wrong, but at first glance it looks to me like a DOS (compatible) kernel without COMMAND.COM support.

Yes it’s a dos compatible kernel (but also Linux compatible) it has a very basic command.com the forks address space to start programs. I use dos navigator as the tui to the os for the retro feel. It DN invokes “command.com /c program.exe” to start programs which forks internally. Look for command.c in the repo it is compiled by Borland c using retro os itself as part of the build to build command. Com . But command. Com is not a shell currently no