raster charts
PC-based chart programs only give you raster charts, which are really just digital images of paper charts. Think of them as "dumb charts." Chart plotters, and here I'm speaking of the type that use C-Map NT chart chips, provide you with vector charts, which you can think of as "smart charts." An example of why a vector chart is better can be found if you select a "heading up" mode rather than a "north up" mode and then proceed south: the raster chart will be displaying all the lettering and numerals upside down while the vector chart will automatically reconfigure the labels. You'll spend somewhat more for the chips than the CD charts, but you'll get more out of them. Another advantage of chart plotters is that they are built for 12 volt systems, unlike most modern laptops which are going to require you to run the inverter or a generator on long passages. I have a laptop on board, as well as a chart plotter, but only use the laptop for email and weather fax because the chart plotter does so much better a job.