# Atrium (Atrium)

> Technical Reference Manual — the Peios web session host: the three-process architecture, logon and session jobs, the shell's state mirror, and the application contract.

The whole book as one markdown file: [/peios/advanced-peios/atrium/print.md](/peios/advanced-peios/atrium/print.md)

Contents:

- 1 [Introduction](/peios/advanced-peios/atrium/introduction/overview.md)
    - 1.1 [Overview](/peios/advanced-peios/atrium/introduction/overview.md)
    - 1.2 [Terminology](/peios/advanced-peios/atrium/introduction/terminology.md)
- 2 [Architecture](/peios/advanced-peios/atrium/architecture/the-three-processes.md)
    - 2.1 [The Three Processes](/peios/advanced-peios/atrium/architecture/the-three-processes.md)
    - 2.2 [Sockets and Descriptors](/peios/advanced-peios/atrium/architecture/sockets-and-descriptors.md)
- 3 [Logon And Sessions](/peios/advanced-peios/atrium/logon-and-sessions/logging-on.md)
    - 3.1 [Logging On](/peios/advanced-peios/atrium/logon-and-sessions/logging-on.md)
    - 3.2 [Session Hosts as Jobs](/peios/advanced-peios/atrium/logon-and-sessions/session-hosts-as-jobs.md)
    - 3.3 [Lifecycle](/peios/advanced-peios/atrium/logon-and-sessions/lifecycle.md)
- 4 [The Shell](/peios/advanced-peios/atrium/the-shell/the-mirror.md)
    - 4.1 [The Mirror](/peios/advanced-peios/atrium/the-shell/the-mirror.md)
    - 4.2 [Windows](/peios/advanced-peios/atrium/the-shell/windows.md)
    - 4.3 [Keybinds](/peios/advanced-peios/atrium/the-shell/keybinds.md)
- 5 [Applications](/peios/advanced-peios/atrium/applications/what-an-application-is.md)
    - 5.1 [What an Application Is](/peios/advanced-peios/atrium/applications/what-an-application-is.md)
    - 5.2 [The Manifest and the Catalogue](/peios/advanced-peios/atrium/applications/the-manifest-and-catalogue.md)
    - 5.3 [The SDK](/peios/advanced-peios/atrium/applications/the-sdk.md)
    - 5.4 [The Bus](/peios/advanced-peios/atrium/applications/the-bus.md)
    - 5.5 [Capabilities](/peios/advanced-peios/atrium/applications/capabilities.md)
- 6 [Failure Modes](/peios/advanced-peios/atrium/failure-modes/cannot-log-in.md)
    - 6.1 [Cannot Log In](/peios/advanced-peios/atrium/failure-modes/cannot-log-in.md)
    - 6.2 [The Shell Loses the Session](/peios/advanced-peios/atrium/failure-modes/the-shell-loses-the-session.md)
    - 6.3 [Applications That Fail](/peios/advanced-peios/atrium/failure-modes/applications-that-fail.md)
- Appendix A [Message Reference](/peios/advanced-peios/atrium/message-reference.md)
- Appendix B [Constants and Paths](/peios/advanced-peios/atrium/constants-and-paths.md)