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When downloading a big file, can a slow internet connection cause it to corrupt?

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yes i try to download a game i waited and waited thought it was done then it say its corrupted or damage i use a modern and earthlink –  user35893 May 3 '10 at 0:41
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5 Answers 5

up vote 5 down vote accepted

Update: In the first version of my answer, I was confusing Hamming-Code-error detection with the checksum error detection, which is used in TCP/IP. It is much more unlikely, that errors stay undetected, if a checksum is used. Theoretically it should still be possible, if there are errors in the checksum part of the package and in the rest of it. But that is very unlikely. There are other sources of error, which can corrupt data, though.

As mentioned in the other answer, you can detect errors int the downloaded file by checking the checksum of the file (for example MD5SUM).

The reason for data corruption is always a defective connection or another hardware/software error (like a defective file system or hard disk), the speed of the connection is not important. But a defective connection can slow down your transfers and thus result in a slow data transfer.

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Depends how you transfer it: assuming you're downloading using HTTP, FTP, BitTorrent or some other TCP service, all the packets of data will (eventually) arrive intact. It will just take longer on a slow connection.

If you were pulling data down on a V92 modem using kermit or a more primitive mechanism, then transmission errors would be a possibility.

But using internet protocols, the only way you'd have a corrupt file is if the download were incomplete; this could happen if your browser or download-manager is a bit dumb about deciding when the transfer has finished. Then you end up with a short file: the data you have is intact, but you don't have all of it.

If your internet connection is flaky, and you often get disconnected, your software should still be able to cope with that and should just pick up where it left off when you're back online.

The underlying TCP protocol uses a checksum to ensure that each packet (actually a "segment" in TCP-speak) is correct, and will retransmit segments which are found to be corrupt.

Having said all that, it is just possible that some stray cosmic rays could flip a bit in the data as it arrives on disk, so where large files are distributed there's usually a checksum published somewhere: typically it's an MD5 or SHA hash, and you can find software to compute these checksums on your own copy of the file. If your nervous about picking up any old (possibly virus-riddled) free software, then Microsoft provides a checksum tool.

BitTorrent clients use checksums implicitly to guarantee the data is intact.

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Ah, exactly. Incomplete finished transfers. Happened to me on dial-up enough. Sometimes Firefox would just stop a downloaded as finished before it had downloaded all of it. And I've had some FTP upload timeouts on dial-up that made me very mad. Grrr. –  Nathaniel Feb 13 '10 at 22:26
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@Customizer writes: "But they are only able to detect a limited count of errors per packet (only one- or two-bit errors)" -- Are you possibly thinking of ECC checking in RAM modules? Checksums can detect more than one- or two-bit errors. The TCP protocol can also detect other errors besides corrupt packet data, see: tcpipguide.com .

Would have written this as a comment, but the submit button is hidden by the right-hand text column in my browser.

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You are right. Actually, Hamming Codes are not used for TCP error correction. I will correct my answer. –  Customizer Feb 13 '10 at 19:03
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Yes, it's certainly possible. Recently I heard of someone that was having similar issues and it turned out it was only files they downloaded while using a specific ISP. While that's less likely it's worth keeping in mind.

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yes it can... Your computer gets files from server in sort of data packets,if any kind of disconnection occurs during data transfer because of slow connection,this means that there MAY be an error in your file.

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