Some USB devices require more power than is permitted by the specifications for a single port. This is common for external hard and optical disc drives, and generally for devices with motors or lamps. Such devices can use an external power supply, which is allowed by the standard, or use a dual-input USB cable, one input of which is used for power and data transfer, the other solely for power, which makes the device a non-standard USB device. Some USB ports and external hubs can, in practice, supply more power to USB devices than required by the specification but a standard-compliant device may not depend on this. COUNT 4
QSN1 Some USB devices require what? ANS1 more power than is permitted by the specifications for a single port. QSN2 Some devices such as an external hard and optical disk drive can use what? ANS2 an external power supply QSN3 What is another alternative for power for an external hard and optical disk drive? ANS3 a dual-input USB cable QSN4 What is the purpose of a dual-input USB cable? ANS4 one input of which is used for power and data transfer, the other solely for power