USB GPS Comparison
USB GPS receivers are devices that need to be connected to the USB port of a laptop computer to function. While one could be connected to a PDA, this setup isn't practical and generally isn't done. This type of unit is sometimes called a "mouse GPS" as it resembles a computer mouse. It is a GPS receiver contained within a plastic housing with a cable attached. Most have a magnetic base with which to attach to the body of a vehicle.
Also, most have some sort of rubberized base to minimize sliding around when used on the dash of a car. Many, but not all, are waterproof. While some models can run on external power supplied by the vehicle, the USB GPS can be powered through the laptop's USB connection. Some models come with navigating software but with most, you need to purchase separate software. Since there is no display screen and usually no software included, prices are relatively inexpensive - often less than $100 US. They perform at least as good as car-dedicated units or handhelds as they can be placed on the part of the dash that has the best "view" of the sky or placed on the outside of the vehicle. If you're going to have a laptop with you in your car, a USB GPS is a good choice.