The USB architecture is a tiered architecture where the USB Host controller controls all the USB bus activities. Up to 127 USB Devices can be connected in a daisy chain format using logical devices like USB hubs, but can not exceed 7 tiers. The host is responsible for device detection (attachment-detachment), dynamically loading the driver (enumeration), dynamically unloading the drivers on device removal, power allocation (bus powered, self powered), and protection against overdrawn current events. The blocks in the drawing marked “Func” in the tiered architecture figure stand for “Functional device”, such as a USB mouse, keyboard, flash drive, etc. One may connect the functional devices through a logical device like a USB hub.