 Later that year, a 21.5-inch "4K" model with a resolution of 4096 × 2304 was released on October 13, 2015 with older Broadwell processors, as the 27-inch counterparts were upgraded that day directly to Skylake ones.The new rechargeable and wireless peripherals were also introduced that day.In 2017 both 21.5 and 27-inch iMacs were refreshed with newer Kaby Lake Processors, new Thunderbolt 3 (USB-C) ports, and Bluetooth 4.2.