Among the nicest features of the Kindle Fire HD models is dual-antenna Wi-Fi, which operates on 2.4GHz and 5GHz bands simultaneously to deliver 40 percent greater Wi-Fi bandwidth, according to Amazon. We've tested this on other devices and it works great, provided there's a supported Wi-Fi access point. Neither Apple nor Google offer dual-band Wi-Fi. Additionally, both Amazon devices include a micro-B USB 2.0 port for both moving files and charging via the included adapter or a computer. The Nexus 7 provides this port too but can only charge from the AC adapter; the new iPad uses a proprietary 30-pin connector and has no access to the file system. Apple and Google put GPS receivers, accelerometers, gyroscopes and ambient light sensors into their devices; Amazon didn't. Amazon put a Micro-HDMI output port on both new devices; Apple and Google didn't, but Apple offers an optional adapter. Amazon and Apple offer Wi-Fi and 4G models (8.9-inch only); Google plans to do so later. All four devices offer some variety of Bluetooth. And, there are now seven Amazon Kindle models; Apple offers two iPad models and Google has one.