The adapter is backwards compatible. Please keep in mind that if you connect a USB adapter to a low speed USB port, you will be bottlenecked by the limitations of the port and may not take full advantage of the adapter's capabilities. The same applies to wireless connections. You will only connect at the capabilities of the wireless access point or Router you are connecting to. For example, if you are connecting to an 802.11g access point, you will only connect at 54 Mbps.