The exact nature of information exchange in downloads...

[sxyzm]

I have a few questions about the exact nature of downloading.

When you're in a (perfectly legit) bit torrent swarm, you complete a download by exchanging parts of a download with different users, instead of downloading the parts of a file in a straight line. A torrent program can identify which pieces it needs and request them, exchange them, etc. And the graphics of certain torrent programs seem to imply that they very specifically detail the division and assemblage of a file.

Which prompted me to wonder about a few things. First, how single source music downloads work. A music file specifically, because it is a single, homogeneous kind of file...As opposed to a package of program files or something.

The parts must be broken up so that they can be sent remotely...But does it download the data in exact order you would listen to it?

Is the download bar usually an exact measure of download? (Or is it the indication of an exchange? I should probably ask how much so the download bar is a measure of the exchange).

How does your computer calculate the size and percentage of the completion of a download?

 

[AdmnPower]

Well all data being transfered is broken up into things called packets. They are then sent via TCP/IP which is a connection oriented protocol suite that will send confirmations of packets recieved. So in reality your song or program or what ever are already broken down into pieces. What those programs do is assemble groups of packets into pieces that can be requested and then reassemebled into the complete file. Essentially they act as a more bulky version of the underlying protocol that drives the interent in the fact that the pieces are bigger and composed of many packets. So the program will understand what data it has already recieved and what data it sill needs and request the data that it still needs in order to assemble one complete file. Like an assembly line it doesn't matter when all of the parts are recieved as long as when they are all present the package is assembled properly to create one complete file.