How To: Intel iMac Hard Drive Replacement - YouTube
New iMacs use Intel's unreleased Z68 chipset, allows for hybrid SSD-HDD (and may account for SSD iMac delays) - 9to5Mac
iFixit launches Dual Hard Drive Kit and guides for Mid 2011 iMacs - 9to5Mac
iFixit iMac Intel 21.5" Mid 2011 Dual Hard Drive Kit - No Tools - Macfixit Australia
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac
Dead SSD on 2011 Macbook Air Mid 2011 13 Inch? Updated laptop to High Sierra from Sierra, had to go away for a few minutes and came back to the laptop turned