A device instance ID is a system-supplied device identification string that uniquely identifies a device in the system. The Plug and Play (PnP) manager assigns a device instance ID to each device node (devnode) in a system's device tree.
The number of characters of a device instance ID, excluding a NULL-terminator, must be less than MAX_DEVICE_ID_LEN. This constraint applies to the sum of the lengths of all the fields and "\" field separator between the device ID and instance-specific-ID fields.
A device instance ID is persistent across system restarts.
The following is an example of an instance ID ("1&08") concatenated to a device ID for a PCI device: