Operating Systems

The invisible manager between your apps and the hardware. What it actually does, and why you need it.

A program is the recipe sitting on disk; a process is the cooking actually happening. The difference matters.

Many cooks in one kitchen. A thread lets one process do several things at once, sharing the same memory.

How the CPU swaps from one process to another: save everything the first was doing, load back the second — so each resumes exactly where it left off.

They sound identical but aren't. Concurrency = one worker taking turns fast. Parallelism = many workers truly working at the same time.

Two threads change the same thing at the same time — and the answer comes out wrong. A whole update can just vanish.

The fix for race conditions: a lock lets only ONE thread touch the shared thing at a time. Everyone else waits their turn.

RAM is a giant wall of numbered boxes. Each box holds a tiny value, and its number is its 'address'.

Every program is fooled into thinking it owns one big, private stretch of memory — the OS keeps a secret map to where it really sits.

How the memory map is really built: chop memory into fixed-size chunks and keep a lookup list of which chunk lives where.

Your disk is really a huge pile of numbered blocks. The file system is the OS layer that turns it into friendly files-and-folders.

Press one key and watch the whole OS spring into action — interrupts, context switches, process states, and scheduling, all in a blink.