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Thread: File transfer speed - Very simple question

  1. #1 File transfer speed - Very simple question 
    New Member
    Join Date
    Dec 2010
    Firstly, excuse me using UK English, but I was born and raised and reside in the UK!
    Secondly, this is an incredibly basic question and I'm just checking that I got it right!

    Now here's my question:
    If my upload speed has been measured as 1Mbps and I send an email attachment which is 8MB in size, I have calculated that each MB of data should take 8 seconds to upload, so the whole thing should take ~ 1m 12s

    Okay, I am labouring under the impression here that the Mbps in the upload speed refers to megabits and the MB in the file size refers to megabytes
    I am assuming that in this context 8 bits = 1 byte
    1Mbs = 1MB every 8 seconds, or indeed 6.5 MB per minute.

    Is that right?

    The only reason I'm asking is that it took a little longer and I just wanted to check that my calculations are right and that it was just bandwidth fluctuation rather than me not understanding the basic principals of file transfer speeds!

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  3. #2  
    Forum Professor leohopkins's Avatar
    Join Date
    Dec 2006
    Dulwich, London, England
    1Mbps is 1 megaBIT
    8MB is 8 megaBYTES

    8MB in bits is: 8 x 1024 = 8,192Kb x 1024 = 8,388,608 Bytes * 8 = 67,108,864bits

    [* 8 as there are 8 bits in each byte)

    there are 1,000,000 bits in 1 megbit so then do:

    67,108,864 / 1,000,000 = 67.108864s

    time it takes to upload one 8MB file over a 1Mb connection is 67.12seconds

    In future, as a general rule of thumb if Mb has lowercase "b" it refers to "bits", if it is an upper case "B" as in MB, then it refers to bytes.

    You speak of bandwidth fluctuation. - don't forget there are pleanty of other packets and frames hitting your upstream bandwidth than just those of your file.

    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.
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  4. #3  
    Forum Freshman
    Join Date
    Oct 2010
    You cannot count on constant bandwidth even in a network of two PCs connected with Ethernet cable. It varies by tens on KB/s during the transmission process.

    Also count that files occupy a whole cluster on HDD. So if size of your file was 4097 bytes and cluster size was 4096 bytes, then one of the "sizes" would be 8192 bytes. If cluster size if large this could be significant.

    Whether you took TCP overhead in account in your calculations?
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  5. #4  
    Join Date
    Aug 2010
    yeah you are correct with your calculations.
    But the internet speed that your ISP provide you is the speed you get only when everything is in it's best working state.
    So if you are getting 1Mbps internet it may vary from 500Kbps to 1 Mbps.
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