Processes vs. Threads for Scalable Distributed Systems

Handling thousands, or even millions, of simultaneous user requests is a foundational challenge in modern software.

A system's ability to manage these concurrent operations efficiently defines its scalability and responsiveness. This challenge is not just about implementation details; it starts with the fundamental way programs execute on a machine.

In this lesson, we will explore the two fundamental execution models provided by operating systems: processes and threads.

We will learn what each model represents, how they differ in terms of resource usage and isolation, and why these differences are critical when designing scalable systems. Building on this foundation, we will compare multiprocessing and multithreading in practice.

We will then connect these concepts to broader System Design considerations, such as fault tolerance, efficiency, and communication patterns in distributed architectures.

OS-level execution models

At the heart of every running application is an operating system juggling countless tasks. It does this by creating, scheduling, and managing units of execution. The two primary models for this are processes and threads.

A process is a self-contained environment in which a program runs. We can think of it as an independent factory with its own machinery and resources. For example, Google Chrome often runs each browser tab as a separate process.

If one tab crashes, the others remain unaffected because each has its own isolated environment.

A thread, on the other hand, is like a worker inside that factory. Threads operate within the same process, sharing memory and resources but carrying out different tasks. A word processor might run one thread to capture user input while another checks spelling in the background.

This makes threads lighter and faster to create, but also more vulnerable; if one misbehaves, others in the same process can be affected. The illustration below shows how processes reside in memory and how each process can contain multiple threads that execute on the CPU.

Understanding the high-level concepts is a good start, but to make informed trade-offs, we must examine the specific technical distinctions that separate processes from threads.

Distinguishing processes and threads

While both processes and threads enable concurrent execution, their mechanics and architectural implications differ in important ways. The key distinctions revolve around memory usage, resource overhead, and fault tolerance.

Memory allocation and isolation

To understand how processes and threads manage memory differently, ...