Representation of a file in memory

Physical Device Object (PDO)

- Represents media type objects, device type FILE_DEVICE_DISK,FILE_DEVICE_CDROM, FILE_DEVICE_VIRTUAL_DISK etc.
- Created by FSD by IoCreateDevice(..) to represent a physical or virtual disk obj, that it manages.
- At creation time, a VPB (more about this later) structure is allocated and associated with media type objects, by the I/O M.
- Initially VPB flags indicate tht physical media doesn't have any logical volumes mounted (VPB_MOUNTED)
- Later a mount operation might occur.

Logical Volume Device Object (LVDO)

- Represents instance of a mounted logical volume.
- Created by a FSD implementaion.
- As part of mounting the LV, most OS require certain system defined data structs be created and/or initialised to establish linkage b/w the rest of the I/O M structs and in-mem representaion of mounted vol.
- In NT, the I/O M requires that a Device Object representing the mounted LV be created for physical media be created and initialized. For network redirectors, not required.
- Each VDO is logically associated with a PDO using a VPB struct belonging to the PDO. Occurs at mount time, when the very first Create/Open request is received by the I/O M for an object residing on the PDO.