Alex and Emma start with the simplest but most testable idea: an operating system is not the hardware, but the software layer that makes hardware usable. They connect that definition to the evolution from batch systems to multiprogramming, time-sharing, and real-time systems.

This chapter turns from the OS itself to the primary thing it manages: the process. Alex and Emma distinguish a program from a process, walk through the five process states, and then compare FCFS, SJF, and Round Robin in the way exam questions usually demand.

Alex and Emma move from scheduling into concurrency, where multiple processes can access shared data at the same time. They separate the ideas of synchronization, race conditions, and deadlock, then lock in the four deadlock conditions exam questions always want.

This chapter shifts from process behavior to the physical problem beneath it: how the OS manages memory. Alex and Emma unpack paging, virtual memory, and thrashing, with clear distinctions students can reuse in exams.

Alex and Emma finish by comparing monolithic, layered, and microkernel designs, then tying the whole episode back to the OS as a system of abstraction. The ending is built for revision: it condenses the biggest compare-and-contrast questions into a clean final review.