Medianochepaseo70 wrote:
I am still running a 20 inch 2008 iMac with El Capitan 10.11.6, unfortunately I cant afford a new machine at teh moment and I am loosing access to several websites I have accounts with as the software I run is no longer supported. I cannot upgrade my desk top but wondered if I could run a newer soft ware package on a stand alone drive as a start up until I pull together the cash I need.
No. There is nothing you can do to that particular Mac that will enable you to keep pace with current internet security standards. The computer can run no OS newer than the Mac OS X 11 El Capitan that it is already running, regardless of whether it is installed on the internal drive or an external drive.
Your only option to keep up will be to purchase a newer Mac.
Since money is a concern, I'd recommend you look at the offerings at Apple's Certified Refurbished Macs website. For a respectably low price you might get your hands on a fairly new Mac mini which, when coupled with a $100 monitor would serve you well for many years.
Refurbished Mac Deals - Apple