This book introduces our everyday computer systems from the perspective of a professional software user rather than a service user. You will be learning the fundamentals that a professional software user needs and then have greater control over the software you use.

As of August 28, 2021, members of IT50 are no longer anonymous.

• English (unfinished)
• 简体中文（未完成）
• You add it!

We are open to accept new contributors and unsolicited commits.

Before you start writing, please compare the following table of contents with the existing documents in the language you plan to write in. You may start a new chapter or revise existing ones.

The English version takes precedence. If you plan to start a chapter that currently does not exist in any language, please use English. If a chapter has an English version, then other versions must translate it. However, revisions on the English version are accepted.

• Data
  • Binary Data
  • Text Encoding
  • File Format
  • Partitioning and Filesystem
• Program
  • Process
  • Operating System
• Cryptography
  • Cryptographic Hash
  • Symmetric Cryptography
  • Asymmetric Cryptography
  • Public Key Infrastructure
• Network
  • Physical and Data Link Layers
  • Network Layer
  • Transport Layer
  • The Barebone Internet
  • Higher Layers
  • Domain Name System
  • Transport Layer Security
  • The Internet

Note: Section overview chapters exist.