A Peer-to-Peer Primer

By Lev Grossman

Napster and Gnutella let users swap data from one PC--or "peer"--to another, without going through a central server. Here's how they work:

NAPSTER

1 Napster is downloaded and installed on a personal computer.

2 The software enables the PC to log on to Napster's server. When a search is made, the server checks its database for any other Napster users who are online and have that file.

3 If the server finds a match, Napster puts the computer that has the file directly in touch with the computer that wants it, and the file is downloaded from one to the other.

PRO

--User friendly, even for relative Luddites --Popular, which means more chance you'll find the songs you're looking for --Napster is run as a business, so customer support matters

CON

--Its directory is stored on a central server. If the server is slow, so is the service --It works only for MP3s, not other files --Too successful for its own good. Banned at 40% of U.S. colleges

GNUTELLA

1 Gnutella is downloaded and installed on a personal computer.

2 A "hello" message is sent to a computer that's already on the network, which forwards it to seven others, letting them know that the first computer is onboard. They, in turn, forward it to six more, which forward it to five more and so on.

3 A request for a particular file percolates through the Gnutella network. When it reaches a computer that has the file, Gnutella connects the two computers directly, and the file is downloaded.

PRO

--Tough to ban because Gnutella files look like ordinary Web traffic --Truly decentralized; Gnutella doesn't rely on any central server --Works for all kinds of files; Gnutella isn't restricted to MP3s

CON

--You need another user to get onto the network --It's a grass-roots effort, which means no tech-support hot line --Gnutella is a work-in-progress, so there are still bugs in the code