A portable storage device includes nonvolatile memory devices to store data, a storage controller, and a bridge chipset. The bridge chipset is connected to a first connector of a host through a cable assembly, detects a resistance of the cable assembly, provides the storage controller with USB type information of the first connector based on the detected resistance, and after a USB connection is established with the host, provides the storage controller with USB version information associated with the established USB connection. The storage controller selects one of a plurality of operation modes based on the USB type information, the USB version information, and a request pattern indicating random or sequential access to the data from the host, selects clock signals having maximum frequencies in a range within a maximum power level associated with the selected operation mode, and performs power throttling based on the selected clock signals.