This IMac Retina 4K 21.5 inch screen desktop computer is a powerful and stylish machine that is perfect for any home or office setup. With its powerful Intel Core i5 5th Gen. processor, 8 GB of RAM, and 931 GB of HDD storage. The 21.5 inch screen size provides a stunning visual display, while the sleek and modern design of the IMac makes it a great addition to any workspace. This Apple desktop computer was released in 2015 and is packed with features and capabilities that make it perfect for a wide range of applications. Comes with USB Mouse, USB Keyboard, external hard-drive, and external CD disc. This device is used, but all previous documents and files have been removed. All existing programs remain. Sorry I do not know the operating system version.