This was a question over in a different thread, but since it's technical I'm putting it here.
One thing I don't understand is the number of dvds that are posted here as share hashes but then never seem to emerge here, or possibly elsewhere, as torrents.
I didn't understand your comment about the share hashes though. I had just assumed that as (I'm guessing here) quite a few people must d/l via share, almost inevitably somebody would transform the d/l into a torrent and post it here. Or somewhere, so that it would eventually arrive here.
I'll try to explain it as concisely as I can.
Both Share and torrents work with "swarms" of peers. With Share, when a file is first uploaded,
it is split up and distributed to many peers (even if only a couple people are downloading the file)
so that each peer in the swarm only stores and shares a small part of the whole file (
low disk and low bandwidth cost per peer). Of course if the file becomes popular, more peers will have more fragments, just like with torrents. But the key is that it also works well with less popular files, because you still get all the benefits of having a large number of peers from that first distributed upload.
With torrents,
peers are part of the swarm only if they want to download the file (eg: if they add the torrent to their client). With popular files this distinction is not important. But with less popular files, this means the swarm will be very small. Since the only peers are the ones that want to download the file in the first place, they each require more storage space; and if the swarm is small, each peer must also upload more (
high disk and high bandwidth cost per peer, in small swarms). Therefore unpopular files suffer, to the point that 1 seeder and 1 leecher is merely a direct file-transfer, and if the leecher leaves while a second leecher joins, the seeder must start all over.
For torrents to be efficient like Share with unpopular files, you would need (for example) 100 peers to each download only 1% of a file and to donate a (small) amount of bandwidth to each seed their 1%. But nobody does that; it's just not how torrents work. So swarm size and torrent maintenance are inversely proportional. That's why few people are motivated to create torrents if only a couple people want the file; most uploaders stick to files they know will be popular, and use file-hosting for less popular files.
So the fundamental difference is that torrents depend highly on (average)
ratio; but with Share, ratio is not important, just as long as all the
pieces of a file are available, and you donate some bandwidth to the network once in a while.
As a point of reference, Share does have its problems. If no one downloads a file for a period of time, pieces of the file will begin to disappear as they are replaced with newer uploads; and just like torrents,
late peers will be left with incomplete files. People on 2ch often post "reseed" requests just like people do here with torrents.
To combat this, PerfectDark (which is supposed to eventually replace Share) requires "donated" storage space (to the tune of 40GB) in addition to Share's "donated" bandwidth. As you can imagine, with 100,000 peers, the network would have a 4 petabyte (4,000,000GB) virtual hard drive to store all the files. You get the efficiency of large-swarm torrents, full "complete file" availability even for unpopular files, and a host of anonymity improvements (through more effective network obscurity).
