Can someone help me on PnPDeviceID ?

[Eric M]

When I get PnPDeviceID from devices such as USB Keys, I get strange data,
especially after the last "/" . I have concluded an empiric rule: if there
is only one "&" character, the USB Key PnPDeviceID is the same whereever I
connect it (other port, computer), else it is dependant (if I want to make it
independant, I have to do not take into account what is after the first "&"
character.
I found no explanation on PNPDeviceID structure. Can you help me ? Why are
they different structure from manufacturers ? Is my empiric rule correct ?
Any help would be appreciate.

Thanks,

Eric.

[Pavel A.]

a great observation :)

In case where there is one &, the PnP ID contains so called "serial number" of USB device.
Devices with serial numbers have same PnP IDs when connected to any port.
Actually "serial number" can be (almost) any character string, not just number.
Devices that do not have such numbers have a "cryptic" ID, and it will change when
device is attached to different ports.
Most cheap USB devices do not have serial numbers because this would
add few cents to the manufacturing cost.

Regards,
--PA

Post by Eric M
When I get PnPDeviceID from devices such as USB Keys, I get strange data,
especially after the last "/" . I have concluded an empiric rule: if there
is only one "&" character, the USB Key PnPDeviceID is the same whereever I
connect it (other port, computer), else it is dependant (if I want to make it
independant, I have to do not take into account what is after the first "&"
character.
I found no explanation on PNPDeviceID structure. Can you help me ? Why are
they different structure from manufacturers ? Is my empiric rule correct ?
Any help would be appreciate.
Thanks,
Eric.