How Computers Work

How a Computer Works

Core Components

CPU Internals

• ALU (Arithmetic Logic Unit) — performs math and logic operations
• Control Unit — fetches and decodes instructions
• Registers — tiny super-fast storage (8-64 bytes)
• Cache (L1/L2/L3) — faster than RAM, slower than registers

Fetch-Decode-Execute Cycle

1. FETCH    → Read instruction from RAM at address in Program Counter
2. DECODE   → Decode what operation to perform
3. EXECUTE  → ALU performs the operation
4. STORE    → Write result to register/memory
5. INCREMENT PC → Move to next instruction

What Is an Operating System?

An OS is software that manages hardware resources and provides an environment for applications to run.

OS Functions

1. Process Management — create, schedule, terminate processes
2. Memory Management — allocate/deallocate RAM, virtual memory
3. File System — organise files on storage devices
4. Device Management — drivers, I/O operations
5. Security — access control, user isolation
6. Networking — TCP/IP stack integration

Kernel vs User Space

User Space:   Applications, shells, libraries (restricted access)
─────────────────────────────────────────
Kernel Space: OS core, device drivers (full hardware access)
              Handles: syscalls, interrupts, hardware abstraction

User programs request kernel services via system calls (syscalls): open(), read(), write(), fork(), exec().

Processes & Threads

• Process — an instance of a running program with its own memory space
• Thread — a lightweight unit within a process sharing its memory
• Context switch — OS saves state of current process and loads another

# View processes
ps aux
top
htop

# Process tree
pstree

OS Families