EveryMac.com wrote:
The iMac "Core i5" 3.2 27-Inch Aluminum (Late 2013/Haswell) features a 22 nm "Haswell" Quad Core 3.2 GHz Intel "Core i5" (4570) processor with four independent processor cores on a single chip, a 6 MB shared level 3 cache, 8 GB [this offering has been upgraded to 16GB] of 1600 MHz DDR3 SDRAM (PC3-12800) installed in pairs (two 4 GB modules), a 1 TB (7200 RPM) hard drive, and a NVIDIA GeForce GT 755M graphics processor with 1 GB of dedicated GDDR5 memory. It also has a built-in "FaceTime HD" webcam and stereo speakers, but lacks an optical drive.

This model has a 27" 2560x1440 LED-backlit 16:9 widescreen IPS display with the "cover glass fully laminated to the LCD and anti-reflective coating." The rear of the case is aluminum and is thicker in the middle and tapers to a razor thin 5 mm at the edges.

Connectivity includes:
* four USB 3.0 ports,
* dual Thunderbolt ports,
* Gigabit Ethernet,
* 802.11ac Wi-Fi (802.11a/b/g/n compatible), and
* Bluetooth 4.0.

Compared to its predecessor, this model essentially has the same external enclosure, but it has a much more efficient "Fourth Generation" processor and architecture, as well as faster graphics, faster Wi-Fi, and the option of faster storage.