I've heard of Types 1 and 2 - removable and nonremovable from their caddies, or is it the other way round? - but I've now found double-sided disks at a good price, apparently in caddies, which are specified as Type 4. What does that mean? Oh, and Verbatim is supposed to be one of the better brands, right? Even if Panasonic want me to use theirs...?