How To Make A Certain Partition Inaccessible By User

I'm planning on installing a fully new OS on a friends computer which he shares with his family, I wanted to make the OS only accessible to him by adding a password but the purpose of this is to keep his content safe. His family could still access the partition that his OS is on and delete some of his things so I want to make the drive inaccessible. I know this can be done as I've seen it done on school computers, accessing a drive will prompt you with a message saying access to this partition has been disallowed to you by the admin or something along the lines. Only other info I know is that files can be accessed in that partition through a shortcut, but you cannot go into the partition itself. The schools also had a security system that prevented you from opening any .exe file unless it is specified somehow (eg. MS office).