The iMac "Core i5" 3.1 21.5-Inch Aluminum (Retina 4K, Late 2015/Broadwell) features a 14-nm "Broadwell" Quad Core 3.1 GHz Intel "Core i5" processor (5675R) with four independent processor "cores" on a single chip, a 4 MB shared level 3 cache, 8 GB of onboard 1867 MHz LPDDR3 SDRAM, a 1.5 TB of flash storage, and an "integrated" Intel Iris Pro 6200 graphics processor that shares system memory. It also has a built-in "FaceTime HD" webcam and stereo speakers.
This model has a 21.5" 4096x2304 LED-backlit 16:9 widescreen IPS DCI-P3 "Retina 4K" display (that runs "pixel doubled" to look like 2048x1152). 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 2 ports, Gigabit Ethernet, 802.11ac Wi-Fi (802.11a/b/g/n compatible), and Bluetooth 4.0.