The previous part followed a single packet from copper wire to NVLink, all the way across the network stack. This part zooms back to one machine and asks: what turns a pile of hardware sitting on a desk into a computer?
The answer is the operating system. It is the first program that runs after the BIOS hands control over, and from that moment on, every other program on the machine is running on top of it. The OS is the bodyguard, the scheduler, the memory manager, the file system, the security boundary, and the abstraction that lets your Node.js process talk to a network card without knowing it is a network card.
A note on order
Topically, this part sits before networks. You boot the machine, then it sends packets. We placed it as Part 04 instead of inserting it between Part 02 and Part 03 because re-ordering would have broken every existing URL into the networks chapters, and we cared about that. You can read this part before Part 03 if you prefer the topical flow — it stands alone.
Pratik's voice continues here. The same rules apply.
Do not trust this book. Validate everything in it.
Do not skip the struggle. The homework at the end of each chapter is the actual chapter. Boot a kernel. Crash an OS. Create a zombie process. Run a Docker container next to a virtual machine and notice the difference. The reading is just the prompt.
Turn the page.