Many USB 2.0 WiFi dongles, such as the Archer T3U Nano by TP-Link, are associated with claims such as:
Nano Sized USB Adapter – AC1300 Dual band for fast and high speed Wi-Fi connection (867 Mbps on the 5 GHz band or 400 Mbps on the 2.4 GHz band)
However, USB 2.0 rate is around 480 Mbps, so what does the "867 Mbps" on 5GHz band even refer to? Is it the theoretical data rate for the adapter-router communication channel?
That interpretation would not really make sense in practical terms, since the adapter is on USB 2.0 and can transmit data at most 480 Mbps (leading to packet loss or buffer overflow if data is incoming at a rate of 867 Mbps). What would happen in practice if the incoming data rate was really 867 Mbps?
Best Answer
While you are indeed limited to an average data rate of 480MBps, the over-air data rate could indeed be 867Mbps.
They are two distinct links. From your computer to your wifi card will only manage 480Mbps (minus some amount of overhead) but the Wifi card could be able to buffer some small amount of packets and transmit those packets in bursts at 867Mbps. I would not expect it to buffer particularly much, maybe in the order of 10-100kilobytes, definitely not megabytes but certainly a packet or two of 1500bytes.
To you as a user there is no real difference in that you only see the USB 2 data limit at around 480Mbps (megabits per second) which ends up somewhere down at 35 to 40 megabytes per second.
To other users of that wifi spectrum though they see periods of time where there is usage at the high speed, but they also see periods of inactivity where they themselves could get their data sent.