Apple iMac 27" Core i5-2500S Quad-Core 2.7GHz 4GB RAM 1TB HDD All-in-One Computer. 

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.

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".

Key Features:

• Aluminum design
• Intel Core i5-2500S 2.7 GHz quad-core processor
• 3.7 GHz Max Turbo Frequency
• 6 MB Intel Smart Cache, 5 GT/s DMI
• 4 GB RAM (supports up to 32 GB RAM )
• 1 TB HDD 
• Slot-loading 8x DVD¬±RW DL SuperDrive
• AMD Radeon HD 6770M with 512 MB of GDDR5 memory
• Built-in stereo speakers with 17-watt digital amplifier
• Built-in microphone
• Built-in 10/100/1000BASE-T Gigabit Ethernet
• Built-in AirPort Extreme (802.11n)
• Built-in Bluetooth 2.1+EDR (Enhanced Data Rate) module
• Built-in FaceTime HD camera
• SDXC card slot
• Built-in 27-inch glossy LED-Backlit widescreen TFT active matrix LCD display (2560x1440) with IPS technology
• Mac OS 
• Model : MC813LL/A