A download manager devides downloads in pieces, and downloads them
simultaneously.
actually anything that manages downloads is a download manager. what
you are referring to is a multi-threaded download manager.
If you have plenty of bandwidth, you can increase your
speed by downloading sceral pices of a file at the same time.
more importantly, you are distributing the load over several inet pipes.
so downloading half from mirror A, and half from mirror B, can often
be faster than only using mirror A. this only works when your bandwidth
is higher than the target's effective bandwidth.
But you can
only download something on the maximum of your modems speed. If you're
alreay downloading at your maximum speed, deviding the download will not
help increasing the speed. This is, in my experience, 999 out of 1000 times
the case with dial-up.
However, a download manager can be very helpful for people on dial-up to
set a download at a time you prefer downloading something, and resume
partially finished downloads.
a downloader with resume feature e.g. wget. this makes even 650 meg
ISOs possible on dialup.
the best upgrade on dialup is probably a v 92 modem. it will increase
the upload speed substantially, and potentially adds more compression on
download. obviously compressed archives can't be further compressed[1],
but text can be.
michael
[1] to any noticeable degree