You can create a limited (regular) user account for him.
Only Administrators can format disk drives.
Therefore he won't be able to format a drive. Formatting USB drives also requires Administrator privileges.
There are no special privileges for formatting in Windows: all or nothing. So you can't select drives where formatting is allowed.
Beware: non-Administrator user account imposes other restrictions as well: installing software (desktop), changing global system settings…
I was thinking about other ways on how to prevent drive formatting. (Although these options are more about making it harder to see the drive, as a side effect you get the bonus of preventing formatting.)
- Hide the drive from Explorer, as User suggested. The drive is not visible in Explorer interface but it's accessible through the system. Other application may show it. And you can easily get access to it: type
D:\ in the address bar, and here you go.
- Hide the drive entirely, remove drive letter association.
- Click Manage in the context menu of Computer.
- Select Disk Management in the list of options on the left.
- Right-click the box with drive
D: (or any other) and then click Change drive letter and path.
D: and click Remove button.
To restore it, click Add and assign a drive letter.
- Remove Format command from drive context menu. Yet I haven't found a way to do it.
When you remove drive letter as described in option 2, no one can access the drive in Windows. You have to add a drive letter to use it.
Yet there's alternative: you can mount the drive into a folder.
In the dialog from step 2.4, click Add, click Mount in the following empty NTFS folder, and type the path to the folder or click Browse to select it.
This way the drive can't be accessed via a drive letter (if it's unassigned of course), but all the data from the disk is visible in the folder.