External hard drives

You can connect as many external drives as you have places to connect them, then buy a Dock and connect even more.

You need not install MacOS (any version) on any added drives.

Best Practice is to use Disk Utility to completely ERASE a new drive using its immutable manufacturer device-name, not just its user-created name like Macintosh HD. DON'T use the drive-maker's Utilities.

Readers are eager to provide additional assistance if you get stuck.

NO it is not Installing MacOS that will allow the drive to be seen and manipulated. It is being ERASED with Disk Utility, the application that bridges the worlds between raw drives and Mountable Volumes.

a drive is only USEABLE with a Mac AFTER you launch Disk Utility, select the drive by it immutable manufacturer's device-name, and choose ERASE.

OR specify that as the drive to be used in Time machine, and time machine will launch Disk Utility for you.

Many drive manufactures have a bad habit of pre-placing stuff they think you should have on their brand new drives,

MacOS does not want you to erase "by acccident" if you really wanted to keep that stuff, and because it is often in Windows format, throwing away all the files to clear the drive before ERASE is difficult.

So ERASE the drive again. When it give you an error message, then, without any intervening operation, tell it to ERASE the drive again. Often, this will let it know you are serious and go ahead and ERASE.

For Monterey it's GUID and APFS.

(for MacOS 10.12 Sierra and OLDER its GUID and MacOS Extended HFS+ )

try this setup-by-step:

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

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Victorybabe67 Said:

"External hard drives: Can an external hard drive be connected to my MAC running macos monterey? Also, do I install macOS Monterey on the hard drive?"

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For note:

Drive Incompatibility:

Vintage drives that use an IDE cable, likely not. As for a newer drive, if it is Windows only, then no. It will not work. So, look at the manufacture, and model, and do bit of research, in terms of compatibility. Report back what you find.