2 versions of OSX on an iMac 2011

[Harrie van Beurden]

My iMac 21.5", medio 2011, Processor: 2,5 GHz Intel Core i5, RAM: 20 GB 1333 MHz DDR3, 500GB SSD (261 GB free) still runs on OSX ElCapitan 10.11.6 for a reason. I can’t afford to loose 10.11.6 because my legal copy of Adobe Photoshop CS6 will not run well on newer OSXs.

Since I have ample space to do that, I want to make a new partition on my SSD and install High Sierra, 10.13 for normal uses and keep ElCapitan for photo editting.

Q: can I just do that?

Q: How much space should I use for the new partition?

 

[Fishrrman]

I realize you have only USB2, but I'd suggest "another way":

Get a medium-sized USB3 external SSD (500gb), and put High Sierra on that.

I predict this will be a better solution than re-partitioning the internal drive.

Does the 2011 iMac have thunderbolt?
You could try to find a thunderbolt external SSD, which would run a little faster, but they're more expensive (IF you can even find one).

 

[Harrie van Beurden]

Are you really suggesting that an USB3 external SSD could run faster/better than the internal one?
I don't understand, because I always thought that the internal SATA disk was the way to go for System and programs. And even if the external SSD had USB3, I can only plug it into a USB2 slot.
So I'm a bit confused.

I've got 2 internal disks: a 500GB SATA SSD and the original 500GB SATA HD, side by side.
OSX and all software are on the SSD, the HD is used for storage only and everything is backed up to an external 3TB HD.

And yes, my iMac has a thunderbolt port, but I never found any use for it.

 

[Fishrrman]

"I've got 2 internal disks: a 500GB SATA SSD and the original 500GB SATA HD, side by side.
OSX and all software are on the SSD, the HD is used for storage only and everything is backed up to an external 3TB HD."

In that case, I'd put the copy of the OS that "I use and value most" on the SSD drive, and the other OS on the other drive.
Sounds pretty simple to me.

You could partition the SSD if you want, and install a version of the OS to each partition.
However... if you're going to use High Sierra, I'd do an "HFS" install rather than APFS.
I just don't see both HFS and APFS boot OS's co-existing on the same drive without inviting problems somewhere down along the line...

 

[RogerWilco6502]

My iMac 21.5", medio 2011, Processor: 2,5 GHz Intel Core i5, RAM: 20 GB 1333 MHz DDR3, 500GB SSD (261 GB free) still runs on OSX ElCapitan 10.11.6 for a reason. I can’t afford to loose 10.11.6 because my legal copy of Adobe Photoshop CS6 will not run well on newer OSXs.

Since I have ample space to do that, I want to make a new partition on my SSD and install High Sierra, 10.13 for normal uses and keep ElCapitan for photo editting.

Q: can I just do that?

Q: How much space should I use for the new partition?

A) Yes you can, I have done it on my MacBook with Snow Leopard and El Capitan.

B) I'd say start out with half and half and then adjust as necessary. Just make sure to back up any data before partitioning

 

[Harrie van Beurden]

In that case, I'd put the copy of the OS that "I use and value most" on the SSD drive, and the other OS on the other drive.
Sounds pretty simple to me.

You could partition the SSD if you want, and install a version of the OS to each partition.
However... if you're going to use High Sierra, I'd do an "HFS" install rather than APFS.
I just don't see both HFS and APFS boot OS's co-existing on the same drive without inviting problems somewhere down along the line...

Thank you Fishrrman!
I'm a Mac-user since way back when 1MB RAM and 40 MB diskspace was the talk of the town. When my model SE came the size of a shoebox, the monochromtic display the size of a postcard, and mice were only known (and hated) as unwelcome rodents.
But tampering with the innards of the beast never was my hobby. So thank you for setting my mind at ease, over this dilemma.
[automerge]1583167780[/automerge]

A) Yes you can, I have done it on my MacBook with Snow Leopard and El Capitan.

B) I'd say start out with half and half and then adjust as necessary. Just make sure to back up any data before partitioning

Thank you Roger,
I'm not well versed in computer technology, so I felt it would be better to ask, before I destroyed my system.

 

[RogerWilco6502]

Thank you Roger,
I'm not well versed in computer technology, so I felt it would be better to ask, before I destroyed my system.

No problem, it's always good to ask if you're unsure. I've done a lot with partitioning my Macs and even I make mistakes, so it's always better to be safe than sorry