> For the complete documentation index, see [llms.txt](https://docs.verifone.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.verifone.com/adk-os-platform/user-guide/readme.md).

# VOS3 User Guide

## VOS3 User Guide

Use this guide to understand how VOS3 devices are built, secured, updated, and operated.

VOS3 is a Linux-based platform with a dual-processor architecture, authenticated software installation, and SDI-managed secure services.

### Who this guide is for

This guide is most useful for:

* application developers
* solution architects
* service and support engineers

### Platform at a glance

Key VOS3 concepts:

* the application processor handles runtime, UI, and communications
* the secure processor handles protected input, card interfaces, and key operations
* software installation uses signed bundles and an A/B update model

### Core topics

Start with the topic that matches your task:

* [System overview and architecture](/adk-os-platform/user-guide/readme/system-overview-and-architecture.md) — platform model, supported devices, processors, services, and control panels
* [Security and system protection](/adk-os-platform/user-guide/readme/security-and-system-protection.md) — overview of the platform security model, cardholder data protection, and key management topics
* [Lifecycle, modes, and startup](/adk-os-platform/user-guide/readme/lifecycle-modes-and-startup.md) — device lifecycle, APP-DEV mode, warrantied keys, and the startup flow
* [Storage, users, and installation](/adk-os-platform/user-guide/readme/storage-users-and-installation.md) — overview of filesystem layout, package formats, signing, and installation topics
* [Device connectivity and card interfaces](/adk-os-platform/user-guide/readme/device-connectivity-and-card-interfaces.md) — communications interfaces, card readers, and SDI card integration points
* [User interface and application control](/adk-os-platform/user-guide/readme/user-interface-and-application-control.md) — UI capabilities, media support, and Multi-Application Controller behavior

### Related guides

Use these guides for development tasks and adjacent topics:

* [Developing Applications on VOS3](/adk-os-platform/user-guide/readme/developing-applications.md) — SDK setup, build flow, packaging, and debugging
* [Migration Guide from Previous Platforms](/adk-os-platform/user-guide/readme/migration-guide.md) — key platform differences and migration notes
* [VOS3 Password Management](/adk-os-platform/user-guide/readme/vos3-password-management.md) — MAC password policy, access groups, and deployment behavior
* [VOS3 Foreign Object Detection (FOD)](/adk-os-platform/user-guide/readme/vos3-foreign-object-detection-fod.md) — FOD control panel, configuration, APIs, and troubleshooting


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