Dual boot - what happens with "Install alongside windows" ??

I was directed here from https://www.reddit.com/r/Ubuntu/comments/5qowau/dual_boot_what_happens_with_install_alongside/

Here's the question I posted there:

I'm following on line guides on how to set up dual boot Windows 10 and Ubuntu. Here's a part I haven't found an answer to.

When I get these options:

* Install Ubuntu Alongside Windows
* Erase Disk and Install Ubuntu
* Something Else

I realize that choosing "Something else" will allow me to set up my swap, root, home, etc partitions as I wish. If I choose the first option though, are there default settings for swap, root, home, etc. that Ubuntu will use? How can I preview the actual disk setup that will be used if I choose the first option?

Also, I see that before starting the Ubuntu install, you need to free up disk space in Windows. That much I understand. But looking at some tutorials like this video (can't post more links here but see my reddit post), when you choose "install alongside windows" it then asks you to divide space between Windows and Ubuntu. See video at about 3:40. Why does it ask about dividing disk space here? If you don't use it all, will the remaining space stay unallocated? EDIT: Or does this option only show up if you didn't allocate free space? And if so, is there a preferred method (allocate space in Windows or do it during the install), and why is it preferred?

TY!

Solution 1:

It doesn't look like there's a way to preview the partitions setup when you choose to "Install Ubuntu Alongside Windows".

I just chose that option, clicked "Continue", and crossed my fingers (I was trying to dual boot Windows 10 with Ubuntu 16.04). I was worried at first Ubuntu would overwrite my Windows recovery partitions, but fortunately, Ubuntu installed itself exactly into the free space I had allocated for it with Windows disk manager (I just followed online tutorials and shrunk my Windows disk); specifically it created one swap partition (same size as my RAM) and another partition for root/home (taking up the rest of the free space). Exactly what I wanted!

UPDATE: Installing Ubuntu 20.04 LTS on a new machine with Windows 10, and there's now a confirmation window once I chose "Install Ubuntu alongside Windows Boot Manager", saying

If you continue, the changes listed below will be written to the disks. Otherwise, you will be able to make further changes manually.

The partition tables of the following devices are changed: /dev/nvm0n1

The following partitions are going to be formatted: partition #6 of /dev/nvme0n1 as ext4 # this is the free space I allocated in Windows

So at least I know this installs Ubuntu in the right partition.