The operating system knows enough to sell you more operating system.

What Windows calls diagnostic data

Microsoft says Windows sends Required diagnostic data about a device, its settings, capabilities and whether it is performing properly. This is the minimum level it says is needed for reliability, security, updates and normal operation.

Optional diagnostic data adds more detail: device health, app activity, software setup and inventory, browsing history, and inking, typing or speech samples in the situations Microsoft documents. Required data remains included when Optional is on.

Microsoft says a device remains secure and operates normally with only Required diagnostic data selected. That makes Optional a real choice for a home user, not a prerequisite for patching the operating system.

Identifiers turn settings into a profile

Windows generates a unique advertising ID for each user on a device. Microsoft says app developers and advertising networks can use it to associate data they hold with that identifier for more relevant ads and personalised experiences across apps.

Turning off the advertising ID does not reduce the number of ads. Microsoft says it stops Windows apps using that identifier, while other interest-based advertising can still be delivered through cookies, third-party apps or Microsoft products.

The important technical distinction is scope. An advertising ID is one identifier; a Microsoft account, browser cookies, app accounts and network activity can each have their own controls and data policies.

Recommendations are a data-use choice

If Tailored experiences—called Personalized offers in newer versions—is enabled, Microsoft says Windows diagnostic data can be used for personalised tips, ads and recommendations. Its examples include suggesting OneDrive when storage is low.

That is a separate product decision from crash reporting. An operating system can collect the minimum data needed to fix updates without treating a storage warning, a Start suggestion or a Settings prompt as a chance to sell more services.

Inspect the payload, not just the toggle

The Diagnostic Data Viewer can display the diagnostic events a device has sent or queued, including a detailed JSON view for each event. It can filter categories and export the stored history as CSV.

To use it, open Settings > Privacy & security > Diagnostics & feedback, enable diagnostic-data viewing, then open the viewer. Microsoft says viewing stores diagnostic history locally and may use up to 1 GB of system-drive space.

Technical users can install Microsoft’s Diagnostic Data Viewer PowerShell module. `Get-DiagnosticData` returns event objects; `Get-DiagnosticDataTypes` maps the event-category identifiers. Run it in an elevated PowerShell session.

A practical privacy baseline

Set diagnostic data to Required in Settings > Privacy & security > Diagnostics & feedback. In Settings > Privacy & security > General, turn off personalised ads that use the advertising ID and review Start and search personalisation.

Turn off Personalized offers unless you want Microsoft suggestions based on diagnostic data. Then review Edge separately: its optional diagnostics are controlled by the Windows diagnostic setting on Windows 10 and 11.

These controls do not make Windows offline or remove every Microsoft service. They do put an explicit boundary between maintaining a computer and turning the person using it into a prompt for the next upsell.