Is it possible to install Mac OS to a hard drive already containing files (with no OS), without first erasing it's files? If so, what is this type of OS installation called?
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Yes, assuming that the disk is already formatted for a Mac. Make sure you backup your files on the disk before performing any OS installation.
I do not know of any special name.
If MacOS has already been installed previously then you can usually reinstall it without any problem. I do it all of the time. All of the activity is done in the system directories and /User directories are preserved.
In the case that MacOS was not installed and there are no /User directories I would proceed with extreme caution unless someone else can verify that it works.
Yes, that will work. If you just have a few random files, or even a few folders, those will remain at the root level of the drive. After a macOS system install, you will simply add the root-level folders: Applications, Library, System, and Users (plus a bunch of hidden folders).
You do run the risk of filling up a drive, as a system install might take up 12GB or more.
AND, you also might have folders already named with the reserved names in the system, which might include Applications, or Library, or var, sbin, usr, bin, private, and a bunch of others that are basic parts of the macOS system. THOSE might get filled with parts of your install; and random folders named Applications, or other names reserved by the system, if at the root level of your drive, absolutely would get files as part of the install, and MIGHT cause you problems as a result.
I would SUGGEST that before you install an operating system of any kind, that you make a new folder with a non-reserved name - maybe with YOUR name, or maybe a pet's name, so you know exactly what that folder is, and is not possibly one used by the system install. Then, drag ALL the existing files and folders on your drive into that new folder.
That should prevent ANY of those files and folders from affecting the install, or your install affecting those folders in any way.
That's what I would do.
You do run the risk of filling up a drive, as a system install might take up 12GB or more.
AND, you also might have folders already named with the reserved names in the system, which might include Applications, or Library, or var, sbin, usr, bin, private, and a bunch of others that are basic parts of the macOS system. THOSE might get filled with parts of your install; and random folders named Applications, or other names reserved by the system, if at the root level of your drive, absolutely would get files as part of the install, and MIGHT cause you problems as a result.
I would SUGGEST that before you install an operating system of any kind, that you make a new folder with a non-reserved name - maybe with YOUR name, or maybe a pet's name, so you know exactly what that folder is, and is not possibly one used by the system install. Then, drag ALL the existing files and folders on your drive into that new folder.
That should prevent ANY of those files and folders from affecting the install, or your install affecting those folders in any way.
That's what I would do.
"Is it possible to install Mac OS to a hard drive already containing files (with no OS), without first erasing it's files? If so, what is this type of OS installation called?"
I'd call it "risky"...
Just kidding, you can do it, but...
... I think the better way would be to do it like this:
1. Copy the files on the drive to somewhere else (another drive, temporarily)
2. ERASE the drive using disk utility
3. Do a clean OS install onto it
4. Get the drive set up with either a new account, or, "migrate" an account from another drive
5. When all this is done and things are "up and running smoothly", NOW it's time to "bring over" the backed-up data from the other drive.
My opinion only.
I'd call it "risky"...
Just kidding, you can do it, but...
... I think the better way would be to do it like this:
1. Copy the files on the drive to somewhere else (another drive, temporarily)
2. ERASE the drive using disk utility
3. Do a clean OS install onto it
4. Get the drive set up with either a new account, or, "migrate" an account from another drive
5. When all this is done and things are "up and running smoothly", NOW it's time to "bring over" the backed-up data from the other drive.
My opinion only.
Yeah i think I'm just just going to move the files and then clean install, just to be sure. I have plenty of drives laying around. It's just an extra step I figured I would avoid, but I'd rather have no doubt in my mind.
Unless there's something special about the drive with files, you could simply install the OS on another drive, then if that works, copy the files onto that. That's only 2 steps, and poses zero risk to the current drive with files (it's preserved even after the OS install). Moving the files off the driver in order to install an OS is an extra step.
Also make sure the OS drive has the GPT partition scheme. It's required for bootability.
Also make sure the OS drive has the GPT partition scheme. It's required for bootability.