Processes vs Threads: Core OS Execution Concepts

An Operating System schedules work as processes and threads:

• Process: An executing program instance. It possesses its own isolated address space, file descriptors, security context, and environment variables. Processes communicate via Inter-Process Communication (IPC) models like sockets or message queues. • Thread: The smallest unit of execution scheduled by the OS kernel. Multiple threads exist inside a single process, sharing the parent process's memory, heap, and open resources, but maintaining their own stack, registers, and program counter.

Context switching is the process of saving a running task's state and loading a different task.

• Process Context Switch: High overhead. The CPU must flush Translation Lookaside Buffers (TLB) and switch memory tables, slowing down the processor pipeline.
• Thread Context Switch: Low overhead. Because threads share the same virtual address space, memory tables remain active, making thread switching extremely fast.

Multi-threaded execution is particularly crucial when building scaling web servers, as detailed in Vertical vs Horizontal Scaling.