Q: how to backup os x capitan onto disk

Disk as in External Hard Drive Disk..?

Or Disc as in CD/DVD Disc..?

Also do you want to backup your Mac or the OS X El Capitan Installer....?

drag the installer

Macintosh HD/Applications/

to your storage device or make a copy of it anywhere but the Applications folder. This needs to be done BEFORE you install it as it WILL DELETE ITSELF from Applications folder once it's installed.

Keep in mind the installer will not fit on a standard DVD-R, it clocks in at over 6GB

Are you trying to back up the computer?

Clone  - Carbon Copy Cloner          (Often recommended as it has more features than some others)

Clone – Data Backup

Clone – Deja Vu

Clone  - SuperDuper

Clone - Synk

Clone Software – 6 Applications Tested

Time Machine Versus Clones and Archives

Commonly Used Backup Methods