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# CGDirectDisplayID

A unique identifier for an attached display.

```
typealias CGDirectDisplayID = UInt32
```

## Discussion

In Quartz, the term *display* refers to a graphics hardware system consisting of a framebuffer, a color correction (gamma) table, and possibly an attached monitor. If no monitor is attached, a display is characterized as offline.

When a monitor is attached, Quartz assigns a unique display identifier (ID). A display ID can persist across processes and typically remains constant until the machine is restarted.

When assigning a display ID, Quartz considers the following parameters:

- Vendor
- Model
- Serial number
- Position in the I/O Kit registry

For information about how to obtain a display ID, see [Finding Displays](/documentation/CoreGraphics/quartz-display-services#Finding-Displays).

---

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