We have restored this computer with a fresh copy of OS X 10.9 Mavericks, and have also included iLife and iWork (2009 versions...sorry this is what I have!)
The iMac "Core i5" 2.7 27-Inch Aluminum (Mid-2011) is powered by a Quad Core 2.7 GHz Intel "Core i5" I5-2500S (Sandy Bridge) processor with a dedicated 256k level 2 cache for each core and a 6 MB shared level 3 cache. In lieu of a system bus, it has a "Direct Media Interface" (DMI) that "connects between the processor and chipset" at 5 GT/s.
By default, it is configured with 4 GB of RAM (1333 MHz PC3-10600 DDR3 SDRAM), a 1 TB (7200 RPM) hard drive, a vertically-mounted slot-loading DVD±R DL "SuperDrive", and AMD Radeon HD 6770M graphics with 512 MB of dedicated GDDR5 memory.
It also has a built-in "FaceTime HD" video camera and built-in stereo speakers underneath the 27" glossy 16:9 LED-backlit TFT Active Matrix LCD (2560x1440 native) display "with IPS technology".
Connectivity includes four USB 2.0 ports, a Firewire "800" port, built-in AirPort Extreme, Gigabit Ethernet, and an SDXC card slot as well as dual "Thunderbolt" ports that are backwards compatible with Mini DisplayPort and, likewise, each support an external display up to 30" (2560x1600). Thunderbolt also supports other peripherals that use the Thunderbolt standard which provides up to 10 Gbps of bandwidth in both directions.
Externally, the "Mid-2011" iMac line uses the same "edge-to-edge" glass design and "seamless all aluminum enclosure" as the "Mid-2010" models that came before them. Internally, however, the "Mid-2011" line is equipped with faster processors and faster graphics processors, as well as the aforementioned external improvements of a higher resolution (and wider angle) webcam and Thunderbolt.
The "Mid-2011" iMac models included a compact aluminum Apple Wireless Keyboard and the choice of either a multi-touch "Magic Mouse" or a multi-touch "Magic Trackpad" that "enables users to scroll smoothly up and down a page with inertial scrolling, pinch to zoom in and out, rotate an image with their fingertips and swipe three fingers to flip through a collection of web pages or photos" just like on Apple notebooks from the same era.