If you only want to format these drives for use with Windows 7, and don't care about any data that is on them currently, there is no need to install any additional software.
Hit the Windows key, type disk management into the search box, and then press Enter. This will present you with a window that will show the disks and allow you to format and/or partition them. You can also set up advanced features like software raid and more from here. The only thing you will not be able to do from here is mount these disks as they are, because about the only file systems Windows understands natively are FAT, NTFS, and the various optical formats.
tl;dr: This is space reserved for metadata storage.
This article about NTFS technical side will give you some more details, but most of this space is taken by the Master File Table. (Some space is also used for the boot sectors, and so on.)
What explains a good part of the "bloated" metadata in NTFS compared to, say, FAT32 is the need to store Access Control Lists - although there are more things in there.
How much space is used by the MFT?
There are 4 settings available when you format a hard disk in NTFS:
- Setting 1 reserves approximately 12.5 % of the volume. (Default)
- Setting 2 reserves approximately 25 %.
- Setting 3 reserves approximately 37.5 %.
- Setting 4 reserves approximately 50 %.
This is because the MFT size is proportional to your number of files. A standard (12.5 %) MFT size will be enough to provide metadata space for all your files if you fill the rest of your disk with 8 KB files. Of course, since some files are going to be much bigger, this is an average.
If you store a large number of smaller files to your disk, there won't be enough space to accommodate all their metadata in the reserved MFT space. This is not fatal, as a new MFT cluster will simply be created elsewhere. However, it will cause MFT data fragmentation, which is bad, as in, can cause severe performance degradation in some cases.
Best Answer
I think what you are asking is impossible to achieve. If a user has admin access to the drive they will always be able to format it. The only way to achieve this is to not allow anyone else physical access to the drive. If someone plugs your drive into their machine they can do whatever they like.