China DOS Union

I ran into the following problems while programming:
1、How can I tell whether a certain sector on the disk is occupied, and how can I search for and locate available disk space?
2、How can I safely move occupied sectors to available disk space (similar to Norton Speedisk)?
3、How can I keep a certain sector from being used by other programs (preferably not even readable)?
4、How can I add and remove bad cluster markers for a certain sector?
My knowledge is not broad, my level is not high, and my experience is insufficient. I ask all the experts here to enlighten me using Assembler/BASIC/C/C++.

To achieve the functions mentioned above, you must be quite familiar with the format used by disks to store files. Also, there are too many file formats now: fat12 fat16 fat32 ntfs, and different file formats have to be handled differently.
If it's only under DOS, it's somewhat easier to talk about.
I suggest you find relevant materials and study them.
In addition, the two articles I reposted, "Detailed Explanation of the Hard Disk Partition Table" and "Introduction to Hard Disk Partition Structure", can also be used as references.
As for how to implement it, you can look at the relevant contents in DOS interrupt calls.