This may sound kind of stupid, but I don’t care 
Anyway, ok, say I got a web site, and start downloading a file. Then, I see another file I like, and I download that too.
How do web browsers like Internet Explorer and Netscape Navigator take the phone signal (for those like me who still use dial up service) and separate parts of it to deal with different things (if that makes since). For example, the downloading of more than one program at a time. How does it know which parts of the phone signal go to each program that’s downloading? Or, I also guess I can ask how, when you have multiple web site windows open, how the browser knows how to sperate the signal for each window.
Thanks.
Short answer: The internet is based off of a protocol called TCP/IP. This protocol breaks up the information into smaller chunks called packets. Each packet has a header that tells the receiver what that packet goes to. Then, your computer puts them back together based on the information in the header.
IE actually spawns a child window (technically more like a sister window) when you start a download or open a new instance of IE. Each window can request information from your PPP transport protocol, which translates the request to the TCP/IP stack (the network layer), which turns that request into something your modem driver (data link layer) can understand, which then communicates with your modem (the physical layer) that can turn that request from digital 1’s and 0’s to an analog signal (the screeching you hear when dialing your ISP).
So in reality IE has no direct connection to the separation of signals. And the modem only knows that it needs to convert digital signals to analog and back again (or MOdulate/DEModulate).
Now that I think about it I believe the OS kernel gets involved between the application and the transport protocol, but lets not get technical.
On preview somebody’s already answered but I’ll post this anyway.
let’s start with an analogy…
Imagine that you wanted to send several books to someone through the mail but you could only send one page per envelope. First you’d make sure every page had a number on it so the recipient could put them back in the right order. Then you’d put the title of the book on the envelope so he’d know which book that page went with. With that done, you could take the whole pile of envelopes to the post office and mail them off. Even if you couldn’t mail them all the same day or even from the same post office, the person on the other end could still put them back together into legible form by using the numbers and the titles. It wouldn’t matter if the envelopes got mixed up on the way to the post office because they’re all marked properly.
How do computers do that? A file is broken into packets (pages) and then numbered sequentially and marked with the name of the file. Each one of those packets is then sent out onto the internet independently with both a destination and return address. When the recipient gets a packet for a multi-packet file, it gets it put aside until all of its other packets arrive. Only then is it actually reconstructed back into a file. Here the analogy breaks down because the receiving computer is smart enough that if a packet comes in damaged (a smeared page), it can send a message back to the server asking for another copy of just that packet. When it finally gets them all, it sends back an acknowledgement to the sender (thanks, over and out).
Even though a single web page may consist of hundreds of individual files, each one of them is sent and acknowledged separately.
Which browser window do they go to? That’s just another number that’s included with the packet – kinda like putting a shelf number on the outside of envelope.
This is pretty simplified but I hope gives you the gist of what’s happening.
Yes, that analogy was an excellent way of taking a complicated explination and simplifying it. Thank you.
Raising his hand
I’m with you on the post office analogy, but still have a question. Suppose I ask horseflesh for a collection of recipes, and fatdave for a set of restaurant reviews. They both separate everything and send them along one page at a time. From the west coast comes Mr. McFeely with the recipes, from the east comes Cliff Claven with the reviews. If they get to my driveway at the same time, how do they avoid bumping into each other and handing me one jumbled packet of paper twice as large as the two separate packets? Are the chances of that so small that it is a non-issue? Or when they do, does a check digit or whatnot tell my pc that the garbled packet is useless and so it never sends a response for those pages? Thanks!
Rhythmdvl