Boot OS X from external SSD

[Fishrrman]

"Would you just delete apps from "macintosh HD" or let them stay there un-used?"

If the internal HDD still has a copy of the OS and apps, just "leave them in place" for now.
It will become your "secondary boot drive".

With a Mac, you always, always, ALWAYS want a fully-bootable second boot source somewhere close-at-hand...!

 

[Ben777]

"Would you just delete apps from "macintosh HD" or let them stay there un-used?"

If the internal HDD still has a copy of the OS and apps, just "leave them in place" for now.
It will become your "secondary boot drive".

With a Mac, you always, always, ALWAYS want a fully-bootable second boot source somewhere close-at-hand...!

Ok Thanks

 

[Ben777]

"Would you just delete apps from "macintosh HD" or let them stay there un-used?" If the internal HDD still has a copy of the OS and apps, just "leave them in place" for now.
It will become your "secondary boot drive".

Update. Everything still works very smooth!

QUESTION: with external SSD, can I have two different OS installed and working on the same iMac?

Let's say, can I have OS 10.8 (Mountain Lion) with apps installed on iMac internal HD, and OS 10.14 (Mojave) installed on the external SSD? Then upon (re)starting iMac choose which disk I want to boot from?

Is this correct? Any problems connected with this model? Thanks a lot!

 

[Fishrrman]

"QUESTION: with external SSD, can I have two different OS installed and working on the same iMac?"

Yes.
The Mac doesn't care "from where" it's booted.
If it finds a valid OS, it will "run with it".