Xbox 360 (Core): The original non-HDMI version of the Xbox 360.
Xbox 360 Pro: Recognizable on the silver colored optical drive rather than white one. It came bundled with a hybrid composite/component cable with optional optical out instead of the composite AV cable included with the Core, and a hard drive of 20 or 60 GB. After July 2007 the motherboard was changed to Zephyr (same as on the first Elite), and thus included HDMI output. From around September same year the Falcon motherboards were used.
Xbox 360 Arcade: Arcade models, which include an HDMI output.
Xbox 360 Elite: Includes a 120 or 250 GB hard drive and has a matte black finish.
Xbox 360 S (Slim): Xbox 360 S consoles feature redesigned internal architecture with the Valhalla motherboard, which allows for around 30% more space than previous motherboards, and the XCGPU, an integrated CPU/GPU/eDRAM chip using a 45 nm fabrication process.