Why do modems go dead when your downloading large files?

[Bellweather]

Physically, what is going on when this happens? It seems to poop out after a long while.

 

[MrTux]

Are you asking why the download speed gradually decreases while downloading a file and sometimes eventually stops all together? If so, it is generally not a problem with the modem. It is most likely the server that you are downloading from. Try some other servers (good ones, like from Microsoft) and see if the same thing happens.