[6.S081](https://pdos.csail.mit.edu/6.828/2019/index.html) (MIT, xv6 RISC-V, 2019), [6.828](http://pdos.csail.mit.edu/6.828/2018/xv6.html) (MIT, xv6 x86, 2018), [CS140e](http://web.stanford.edu/class/cs140e/) (Stanford, RPi C, 2019), [CS140e](https://downey.io/blog/cs140e-writing-an-operating-system-in...) (Stanford, RPi Rust, 2018, more on [HN](https://news.ycombinator.com/item?id=16134618), [Andre](https://github.com/rust-embedded/rust-raspi3-OS-tutorials) (RPi Rust, 2019), [CS140](http://www.scs.stanford.edu/12au-cs140/) (Stanford, 2012), [CS194-24](http://www.cs.berkeley.edu/~kubitron/courses/cs194-24-S13/in...) (Berkeley), [Baking Pi](http://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/) (Cambridge, RPi asm, 2012), [OS from Scratch](http://www.cs.bham.ac.uk/~exr/lectures/opsys/10_11/lectures/...) (Birmingham, more in [HN](https://news.ycombinator.com/item?id=8380822)), [OS Development](http://littleosbook.github.io/), (RIT Stockholm, more on [HN](https://news.ycombinator.com/item?id=13258063)), [these](http://news.ycombinator.com/item?id=4834008) (CMU, UMD, MIT, Stanford, Harvard), [BrokenThorn](http://www.brokenthorn.com/Resources/OSDevIndex.html), [bkerndev](http://www.osdever.net/bkerndev/index.php), [JamesM](http://www.jamesmolloy.co.uk/tutorial_html/) ... [OSDev.org](http://wiki.osdev.org/) is recommended in many sources. Here is a recent roundup on [HN](https://news.ycombinator.com/item?id=22087701), and [another](https://news.ycombinator.com/item?id=22149866) (both Jan 2020). This [textbook](http://csapp.cs.cmu.edu/) provides a recent overview of Unix + C OS.