using bootcamp on imac late 2015 and el capitan ti install windows

without any real info on what you tried or what the problem occurring is see this document

OS X El Capitan: Use Windows on your Mac

FWIW, you have to use Boot Camp Assistant to install Windows. You can't just create a Windows formatted partition and install it. It may have to be on the same partition as OSX.

rflombardi wrote:

I have an imac 21.5 late 2015 and cannot get widows to install ON A SEPERATE PARTITION

What do you mean by a 'separate' partition? On a Fusion drive, your Windows installation is normally on the HDD part. Please post the output of

diskutil list

diskutil cs list

from OSX Terminal.

2015 Macs do not use any external storage to build USB Installers. They use an internal OSXRESERVED partition.

Was the ISO built from a Windows DVD using Create an ISO image for Boot Camp from Windows installation media - Apple Support ?

What is the version of Windows?

Do you have any external storage connected to the iMac?

1. Disconnect all external storage.

2. Download the appropriate ISO from https://www.microsoft.com/en-us/software-download/windows10ISO to your Desktop or Documents folder. Do not mount the ISO. Use a wired network connection, if possible.

3. Run the following two procedures

Reset the System Management Controller (SMC) on your Mac - Apple Support

How to Reset NVRAM on your Mac - Apple Support

4. Run BC Assistant, partition and try to install W10. Disconnnect all external network connections before you choose the Bootcamp partition.

Your Late 2015 iMac does not use external USB to install W10 or W8.1.

Please follow the steps as documented in https://help.apple.com/bootcamp/assistant/6.0/#/bcmp173b3bf2 .

Post back if you run into any issues.

rflombardi wrote:

Did not work??

Which step?

What type of device are you choosing as the destination?

You cannot install Windows 10 on a USB flash drive or an external drive using a Mac.