installing a SSD as main drive I have iMac (27-inch, Mid 2011) 2.7 GHz Intel Core i5 12 GB 1333 MHz DDR3 and I have installed a 128GB SSD into the system. Formatted it for mac and it is sitting empty right now. I have the main 1TB drive still installed and working right now with the OS on it. I would like to install the  OS on it and put all my other files on the 1TB drive that has everything on it including the OS Yosemite 10.10.1 . I have tried to set this up myself but have had to start over and ask for help from you fine people here.
 I got as far as installing the OS on the SSD and it worked fine, did not know how to remove the os from the original HHD  without killing everything on the old HHD so I stopped pretending that I know more then I do. So as it sites right now  128GB SSD and 1TB HHD installed on this computer  I have a time machine backup for the main HHD now.
If you've got a functioning OS on the SSD then you should be able to set this as the boot drive in System Prefs. Boot off it and then use Disk Utility to unmount the 1tb drive. Test everything with the 1tb drive unavailable. If everything works fine without it then you can remove what you want from the 1tb drive.