Getting started with bare-metal assembly
How to create a hello world program in assembly that runs directly on top of UEFI (no operating system!). By Jonas Hvid.
How Operating Systems Work: 10 Concepts you Should Know as a Developer
Helicopter view of various central operating system concepts.
Memory Allocation Strategies (gingerbill)
Introduction to various memory allocation strategies by the creator of Odin, a Handmade Network project.
Memory Allocator Designs
Explains various strategies for memory allocation and shows how to implement these as allocators.
Writing a Simple Operating System from Scratch
How-to book on implementing a basic operating system.
Ben Eater Youtube Channel
Ben Eater's hardware hacking videos
Bitwise Programming Streams
Per Vognsen's low-level programming educational series
Onur Mutlu's Youtube Channel
Lectures about computer architecture by professor Onur Mutlu.