Difference between the Device and Device info record?

Hello Gurus,

I have some queries related to device info records  :

1.I would like to know the difference between the devices and Device Information Records?

2.Do we have the records for Device Info. Records in Master Table EQUI?If not,where are they maintained?

3.Under which scenarios,do we need to create the device information records?

4.Do the equipment no. exists for Device info record in PM application component?

Thanks in advance,

jeany.