There already many viewers available, so let's start from what FSPViewer is not. It is not a program for viewing panoramas on the internet. FSPViewer is designed for viewing local (hard-disk, network or CD) high resolution panoramic images at full screen and with very high image quality. It uses advanced interpolation algorithms to show you smooth images without losing sharpness.
Internet viewers are designed for displaying small images in small windows, since bandwidth is limited. Viewing a panorama at full screen will give you a much more immersive feeling, but it will require much more resources from the computer. The whole image will be loaded in memory and the program will need to write a very high number of pixels, so a fast processor will be needed for smooth panning.
Today's (and tomorrow's) computers have fast processors and a lot of RAM, so it's now possible to write a full screen viewer. FSPViewer can handle images limited only from the available RAM and is heavily optimized so it's fast enough on modern computers. It can even use both processors of a dual core CPU like most modern ones.
FSPViewer - 64bit software