A mid-range model is good for those people who would not like to spend a fortune for their new laptop. A middle range model is not as heavy as a top range model and has a smaller monitor. A middle range model will be a little slower than an upper range model when you consider processor speed and the options of internal media are not as varied as in the upper range model. Lightweight models have the smallest display of all three also the processor speeds are the slowest. The expansion capabilities and built in drives are somewhat restricted and extra drives and other devices are usually on the external side. The main purpose of ultralight models is that more convenient to take along because of their smaller and lighter battery using less power. For more info see notebooks computer