Pioneer Continent

The OS is the resource manager between applications and hardware, using three big mechanisms to turn one physical machine into a usable abstract one: virtualization (multiplexing CPU/memory into a private illusion per process), concurrency (multiple execution flows coexisting safely), and persistence (data surviving power loss). Understand why timesharing displaced batch processing, and the mechanism-vs-policy design philosophy. Classic pitfalls: the CPU is never "given" to a process — it runs in full control until the OS reclaims it via traps and interrupts (limited direct execution); the kernel is not another user program but the privileged shared library plus scheduler underneath them all.