ByteTrail

Level 0 · Module 2

Processes

Understand how the operating system represents, schedules, and isolates running programs.

Difficulty
beginner
Time
10 min read
Reading progress0% read

Not completed

By the end, you can

  • Describe the state and resources associated with a process.
  • Explain common process states and CPU scheduling.
  • Distinguish process isolation from communication between processes.

Summary

A process is the operating system’s representation of a running program. It has an identity, memory, resources, and an execution state that the OS tracks.

Introduction

Module 1 distinguished stored programs from running processes. Now we can look at what the OS must record to keep many processes moving safely.

Explanation

Each process normally has a process identifier, virtual memory, open resources, security identity, and one or more execution paths. A process may be running, ready to run, waiting for an event, or terminated. The scheduler chooses a ready process for a CPU core and later switches to another. Isolation prevents one process from directly changing another’s memory; explicit OS mechanisms allow controlled communication.

Real-world example

A browser loads a page

While network data is unavailable, a browser process can wait. The scheduler gives CPU time to other ready processes. When data arrives, the OS marks the browser ready so it can continue.

Watch states change

process-states.txttext
created → ready → running
                 ↓     ↑
               waiting
running → terminated

Code example

scheduler-trace.txttext
09:00.000  process 42 running
09:00.010  process 42 waits for disk
09:00.010  process 77 running
09:00.018  disk completes; process 42 becomes ready

Common mistakes

  • Assuming every process is executing on a CPU at every moment.
  • Believing process isolation means processes can never communicate.
  • Treating a process identifier as a permanent identity across restarts.

Quiz

Knowledge check

A process requests file data that has not arrived. What should usually happen?

Try it

Classify the states

Classify a music player as running, ready, or waiting while it decodes audio, waits for disk data, and waits for its next turn on the CPU.

Key takeaways

  • A process bundles running state and OS-managed resources.
  • Scheduling moves processes among ready, running, and waiting states.
  • Isolation protects processes; OS facilities enable deliberate communication.
View module overview