why is my download speed 300 - 500 KB/sec when my internet speed is around 30MB/sec?

as the title says.... im downloading a windows iso file from the Microsoft website and its going at around 300KB/sec even though a speedtest says my download speed is around 30-40MB/sec.

im using Mac OS Catalina version 10.15.3 with an Ethernet cable.

4 Answers

  • 1 month ago

    Speedtest is telling you the bandwidth of your connection to its server in bps (bits per second).  When you download a file, Windows is telling you the download speed of the file into your file system in bytes per second (Bps).  Bits are lower case b and bytes are upper case B.  There are 8 bits in a byte.  Additionally there is anywhere from ~1.5% to 20% overhead added to each frame being downloaded that isn't accounted for by Windows.  Information on a network is transferred in small chunks called packets.  The packets can vary in size, but the minimum size is 64 bytes, the maximum is 1500 bytes.  If you transfer a 1GB file via the internet it is divided up into approximately 715K packets.  Each of those packets has a layer of address information added to it in order to route it through the Internet.  Windows doesn't see/know about this overhead because it added/removed at lower layers (driver layer) in the protocol stack.  But, this overhead is sucking up bandwidth on your Internet connection.

    The simple math is to take the download speed from Windows and multiply it by 8 to get the bps download speed.  Lets say Windows is saying 400KBps (400,000 Bytes ps) is the file transfer speed.  400KBps x 8 = 3.2Mbps transfer rate.  

    Then you need to take into account the high likelihood that some of those 715K packets will get lost on the Internet.  The way a file transfer works is that each packet is numbered 1.......715K.  If some of the packets get lost, FTP has the file transfer start (or parts of it) over again.  None of this lower level stuff is known to Windows, it only sees the bytes of the file coming in from the network drivers on your PC.   The file transfer actually happens in chunks, where if one chunk gets messed up only that chunk is retransmitted. 

    Then, as another person said the connection between your computer and the server you're downloading from is only as fast as the slowest link between you and it.  The Internet is made up of millions of connections between computers where not all of them are high speed.  This is a real problem with torrents, in that those are coming from the average Internet users computer which may have an upload speed of 12Mbps or less.

    The other thing to factor in is how busy the server is that you are connecting too?  If it's really busy it won't be giving your download 100% of it's performance.  Servers tend to time slice downloads, meaning if there are 100s of downloads happening at once they send a few packets to you, then a few to the next guy and so on.  The effect to you is the download appears slower.

    Point of all this is that there are a zillion things that are legit reasons why your download is occurring slower than you think it should.  Speedtest is the only legit way to verify your Internet performance.

  • 1 month ago

    the internet speed is the max speed that you can download at, similar to the max speed of a car.

    Some servers (roads in this analogy) set a lower speed limit than the max speed of your internet plan (your car)

    the network speed is only as fast as the slowest connection.

  • 1 month ago

    speed test sites are there to test your max speed, but each internet server will have its own load that may reduce download speeds. This is especially an issue if downloading from a server that gets lots of requests.

  • 1 month ago

    The microsoft website is cucking you

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