What are good resources for learning computer architecture, assembly, and operating systems?

A Unix-like educational operating system is a good next step because you can read and modify working source code instead of starting with a blank page. Work through it in stages: compile and boot it, understand the kernel entry point, trace system calls, then experiment with scheduling, virtual memory, filesystems, and hardware support. Keep the first version small and use emulators and debuggers while developing.

The overall path could be digital logic, computer organization, assembly, C or another systems language, and then operating systems. Since you already know higher-level languages, concentrate on low-level C, pointers, data layout, compilation, and how the linker and loader work. Building small utilities and a tiny bootable kernel will teach more than trying to design a full OS immediately.

For the architecture side, use a course or book that builds a computer from logic gates upward. A hands-on project where you implement the CPU, memory, instruction set, and a simple assembler is especially useful. After that, study bootloaders, linking, executable formats, memory management, interrupts, device drivers, processes, and filesystems before attempting a more complete OS.

Don’t jump directly from learning assembly into building an operating system. First write several small assembly programs so you understand calling conventions, memory, stacks, interrupts, and how programs interact with hardware. Once you start writing larger projects, you’ll naturally see which services an operating system needs to provide. Then you can build a very small kernel and expand it gradually.