Device Manager and NONPRESENT Devices

In writing about the Western Digital "Hard Drive Settlement", I started wondering what brands of hard drives I had. I've got about 6 HDs in external enclosures, but they were in my office and I wasn't. I didn't want to open each case up to see what the drive was, and I didn't want to hook all of the drives up to the laptop.

Instead, I opened up a CMD window and at the prompt I typed "set DEVMGR_SHOW_NONPRESENT_DEVICES=1", hit enter, and then typed "devmgmt.msc" and hit enter again. This brought up Device Manager, as one might expect. I then selected "Show hidden devices" from the view menu.

This allowed me to expand the "Disk drives" category and see all of the "nonpresent" hard drives, which had at least some indication of the manufacturer in the name.

2 Seagates, 1 Maxtor, 1 Quantum, and 2 Western Digitals...

The child process (mmc.exe) inherits the environment space from the parent process (cmd.exe), and since the parent process had the environment variable DEVMGR_SHOW_NONPRESENT_DEVICES set, the child inherited that setting. Running devmgmt.msc started mmc.exe, the Microsoft Management Console executable which is associated with .MSC files. The .MSC instructed mmc.exe to load devmgr.dll, which contains the code to check the setting of the environment variable named DEVMGR_SHOW_NONPRESENT_DEVICES and react appropriately.