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Why is my computer's USB connection slow?

Answer: When you connect a device to your computer via USB, there are typically three components – 1) the computer, 2) the device connected to your computer, and 3) the USB cable. Any of these three components could be the cause of a slow USB connection.

The USB interface was designed to be backwards-compatible. This means newer USB standards are compatible with older devices. For example, you can connect a USB 2.0 device to a computer with a USB 3.0 port and it will work just fine. Likewise, you can connect a USB 1.1 device to a computer with a USB 2.0 port, and it will function correctly.

While USB devices are usually compatible with multiple USB standards, they will only communicate at the lowest speed of the connected components. For example, a USB 2.0 device connected to a USB 3.0 port will only transmit data at a maximum rate of 480 Mbps, which is one tenth the speed of USB 3.0's 4.8 Gbps maximum data transfer rate. Similarly, if the same device is connected to a USB 1.1 port, it can only transfer data at 12 Mbps.

Important: If you connect a USB 2.0 or USB 3.0 external hard drive to a computer with a USB 2.0 or 3.0 port and it seems slow, it could be due to a slow cable, such as a USB 1.1 cable. Since USB 1.0, 1.1, 2.0, and 3.0 cables all look the same, it can be difficult to know what standard a USB cable supports. Fortunately, many cables have the USB standard printed somewhere along the cord. Therefore, you should first look at the cable if your connection is slow. If the cable does not have the USB standard printed anywhere, you may want to swap the cable with a known hi-speed USB cable and see if that improves the performance.

Published: August 17, 2012 — by Per Christensson

Answer from the PC Help Center