Installing alongside Windows or on a separate partition [duplicate]
Solution 1:
Since there are plenty of resources here on setting up a dual boot, especially with a Windows system, I won't duplicate that content here.
However, it seems to me that your question reflects a misunderstanding worth addressing in an answer.
When you select Install Ubuntu* alongside Windows*, the installer automatically creates a separate partition for Ubuntu.
So it's unclear what you have in mind when you say "installing on a separate partition"...
What's the difference between installing Linux alongside Windows and installing it on a separate partition?
The answer is that installing Linux alongside Windows is installing it in a separate partition.
A partition is a section of a storage device that has been formatted with a particular filesystem. Different filesystems have different data structures and features. Windows is typically installed on an NTFS partition. Ubuntu will not work properly (at least not without a lot of complex tinkering) if installed on an NTFS partition; it should be installed on an ext2 or ext3 or ext4 formatted partition or another filesystem designed to work with the Linux kernel.
Installing two operating systems on the same partition, unless you install one of them in some kind of container or virtual machine (a popular solution which, depending on your use case, may be more convenient than setting up a dual boot), is generally a really bad idea even if they are both compatible with the filesystem type. As far as I know, in this scenario the systems' files will be mixed up, and there is a risk that processes will overwrite key files belonging to the other system.
The Ubuntu installer will never try to install Ubuntu in the same partition as Windows (although it may format and overwrite the Windows partition) and if it did, I would consider it to be a serious bug.