## TL;DR
Operating systems manage hardware resources and provide abstractions for applications. Process scheduling, memory management, and file systems are the three pillars of OS design.

## Core Explanation
Process management: PCB (Process Control Block) stores process state. Context switching saves/restores CPU registers. Inter-process communication via pipes, message queues, shared memory, sockets. Threads share address space within a process — lighter weight but require synchronization (mutexes, semaphores).

## Detailed Analysis
Memory: paging (fixed-size pages ← page table → frames), segmentation (logical divisions), TLB (translation lookaside buffer — hardware cache for page table entries). File systems: inodes store metadata, directories map names to inodes. Journaling file systems (ext4, NTFS) prevent corruption from crashes.

## Further Reading
- OSTEP: Operating Systems: Three Easy Pieces (free)
- Linux Kernel Documentation
- Microsoft: Windows Internals