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When you select some files and copy them, the file copying dialog appears with progress bar and speed indicators. But when you select some other files and copy them, another dialog pops up and both seemingly show more than 50% speed slowdown as compared to only a single file copying dialog. I'm fairly sure that back in the days doing this with a floppy disk actually did slow down the process significantly. But is it the case with HDDs and SSDs in modern Windows OSs?

Does copying several batches of files through multiple file copying dialogues slow down overall I/O operation in Windows 7?

For example, let's copy a hundred of 50 MB files from HDD A to HDD B and right after that copy another hundred of other 50 MB files from A to B. So the files aren't small and the slowdown isn't caused by file table stuff issues due to small size. Both disks are 90% empty and contain no fragmented files, so there are no problems coming from that way too. Disks are connected via SATA, and aren't external.

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  • there is a lot to this question that is hardware dependent. for instance if you are copying to a usb2 device with a IO speed of 35MBps, you will have to divide that IO rate by the number of processes. if your copy involves multiple small files, it is more likely to cause conflict when maintaining partition metadata, than a pair of large files, etc. Nov 26, 2013 at 13:29
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    Another thing to consider is, are you copying a bunch of smaller files or a bunch of larger files. Copying smaller files is inherently slower on most operating systems than copying larger files. For example, if I copy 5GB worth of 20MB/each images, it will usually be much slower than copying a single 5GB movie. In my experience, parallel copying of large files is nearly as fast as doing two separate copy operations serially, whereas a bunch of smaller files being copied in parallel is MUCH slower.
    – Trav
    Nov 26, 2013 at 14:01

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Yes, it does, as it's copying 2 lots of data at the same time, and thus takes longer to retrieve each piece of data and then process where that piece of data is going to.

Just like how it would take you longer to put 2 lots of things into 2 boxes compared to a whole bunch of things into 1 box. You have to sort out things when putting things into 2 boxes, while you don't when putting it into one box.

SSDs would cut the time down by a lot as the seek time to get a piece of data is nearly zero. On a Hard drive, the slowdown could be quite a bit depending on where the data is on the disk.

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    Teracopy can help. It queues copy/move operations
    – Chris
    Nov 26, 2013 at 13:30

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