In addition to MIMO technology, the 802.11n-compliant APs have additional radio features that increase the effective throughput of the wireless LAN. Second-generation wireless APs use radio channels that are 20 MHz wide. The channels must be spaced at 20 MHz to avoid interference. The radios of 802.11n-compliant wireless APs can use two channels at the same time to create a 40-MHz-wide channel. The 802.11ac radio of the AP38xx and AP39xx series can use four channels at the same time to create an 80-MHz-wide channel. By using multiple 20-MHz channels in this manner, the wireless AP achieves more than double the throughput. The 40-MHz and 80-MHz channels in 802.11n and 802.11ac are adjacent 20-MHz channels, bonded together. This technique of using multiple channels at the same time is called channel bonding.