I have not compared the speed of actually loading Image Pixel data. Your Viewer takes a lot more time to identify all this information than other Viewer (such as eFilm Lite) that reads this from the DICOMDIR. So in terms of loading the basic Information such as Series Information and # of images in each series.
Slow loading because you load each files in a recursion to rebuild the Series.
DICOMDIR is a standard and a requirement now for CD/DVD Distribution.
