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Help understanding some torrent fundamentals pls...


Bullman

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Hello,

I am new to using torrents and have questions which will help me understand a few basics for how it all works. (I might be asking heaps of stuff but if you can help out on any thats cool).

I will try and explain how I think it works and what I don't know. Be good if someone could fill whatever gaps you can or correct me where I am wrong. It's a bit all over the place so here goes........

I understand the concept of the P2P and sharing files and seeding/leeching etc.

Now when you want to search for a file(s)/movie/program or whatever to downlaod using torrents, you need to search for what you want on specific "torrent servers" (don't know). I don't know which sites are best or really where to lokk for list sof these but I guess if I Google for "torrent servers" I might find something.

When you find what you are looking for at the torrent server site (that may have 1000's of things on it to choose from), you may find serval "links" to something that looks like what you are after for you to choose from. Some sites show the number of size, seeds and leechers (eg. http://www.mininova.org). From this choice you need to pick a "torrent"(?). I guess I would pick the ones that had the most seeds. There is always a chance that what you download icould be garbage anyways (because Im sure some people label stuff as one thing but fill it with junk just to p@$$ people off) so there is always going to be a risk that you waste your time.

Regardless of that, you click on that link and a .torrent file os downloaded to your PC. From what I underastand this is just a "link" that is read by your torrent program on "where to look" for this file. So you load the file in your torrent program and stuff starts downloading and uploading.

What I don't understand is if say, you have found and picked a "torrent" to download from say http://www.mininova.org. Let's say it is listed as:

"GARRYSSHED---Freeware Graphic Program ULTIMATE" 134.23MB

Lets say you start downloading it and you notice all the seeds dropping and eventually you are at a snail pace downloading it.

Can you look for alternate places to download it from and resume your download?

Or is that download uniquiely linked to the .torrent file you originally downloaded from the torrent server (in this case http://www.mininova.org) and is therefore only good for "seeds" "known" by that torrent server?

Or can you try and search for the same file at another torrent server to resume downloading from a completely new list of seeds (and more than what you originally found at the first torrent server you looked at)?

OK there it is. Please pick it apart and give me a hand with what I have worng and don't know.

Cheers

Bullman

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BitTorrent downloads are hashed using SHA-1. If you don't know what hashing is, I suggest you look it up on Wikipedia. Basically it's a way of checking that the files are the same.

If you want to resume your BT download, you have to find an exact copy of the file - with the same hash. If it doesn't have the same hash, you can't resume a download, and you'll have to start again.

Have you read the Slyck guide to BT? You might find that useful.

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I guess I would pick the ones that had the most seeds.

Not necessarily. Just because it has the most seeds, it doesn't mean that any of those seeds are high quality.

Lets say you start downloading it and you notice all the seeds dropping and eventually you are at a snail pace downloading it.

You need never download a single segment of the download from a seed to be able to complete. As long as there is at least one copy of every segment you don't have yet out in the swarm of peers somewhere, you can still complete. It is an all too common misconception that connecting to more seeds is the best way to get better speeds on torrents.

Can you look for alternate places to download it from and resume your download?

Only if the files match EXACTLY. There are two ways of getting those files into your partial complete. One of them involves using a second client (either on the same machine or on a different machine LAN'd to your main one) to resume using the files downloaded via a different source/method and connecting to your main client to integrate.

The site you gave an example of, mininova, is merely an index. It doesn't handle communication between peers at all, so it only knows the counts of seeds and downloaders, not their actual information. A torrent index site is separate from the tracker which coordinates peer connections. You could end up searching on another index and simply end up at the same tracker.

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Just to clarify the whole deal with torrent indexes and trackers:

The tracker URL is specified in the .torrent (while you're downloading, look at Tracker URL in the General tab). The index is the site from which you downloaded the .torrent file. Most trackers also have an index indexing content on it (The Pirate Bay, Demonoid and private sites) but there are many sites that just index content from other trackers (mininova, isohunt et al).

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