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Why Does Copying Files Slow Down?

Many possibilities.

Issues with copying files are most often traceable to hard disk issues, but there are other potential causes as well.
Question: I am experiencing a bog down / hang-up when copying large files; the PC has to be restarted to clear this. Any idea what could cause this annoying problem?

These types of problems are difficult to diagnose even with access to the machine. I’ll offer a list of things that come to mind and what I’d look at in your shoes.

Not surprisingly, the list is long and varied.

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Copying files slows down

The most common causes of this symptom are the internal buffering used by the system or the hard drive being smaller than the size of the file being copied. Other possibilities include disk-surface issues, fragmentation, competing software, and other disk-related hardware.

Buffers and caches

This is probably the #1 cause of this symptom, and interestingly, it’s not a problem per se. It’s more like what’s happening under the hood is becoming visible.

RAM is faster than your disk regardless of disk technology. As a result, when you copy a file rather than writing directly to disk, the system may buffer or cache the data in RAM before sending it on to the actual disk. It can do this quickly, and for smaller files, you’d never know. For larger files, once the buffer is full, you can only continue to add to it as it is emptied, which is throttled by the speed of the destination disk.

So the copy will be fast until the buffer fills up, and slower after.

Sometimes the buffer isn’t in your PC but on the disk itself — or rather the circuitry that interfaces to the disk (known as the disk controller). It’s not uncommon for the disk controller to have RAM buffers built in for this express purpose. The symptom is the same: if the buffer fills up, then the disk can only accept more data at the speed data is written to disk. The only “solution” is to let it take however long it takes.

Hard disk errors

The next thing that comes to mind is a hard-disk issue specifically related to traditional spinning magnetic-media HDDs. This is not a failure per se, and perhaps not even something that Windows will notice.

The magnetic media of a hard disk can become “slightly” damaged. I say slightly because even though it’s damaged, the disk drive can still read and/or write the data if it tries hard enough. Hard enough usually means trying again and again and again until it works. That takes time and can manifest as an unexplained slowdown.

Running CHKDSK (with the “/R” repair option) might help, but might not. CHKDSK, like Windows, doesn’t operate at the low level required to address this type of failure.

How Do I Fix Errors on My Hard Disk? has more ideas on this direction of investigation.

Free space and fragmentation

An exceptionally fragmented or nearly full disk can also show signs of slowing down.

While rarely needed anymore (Windows does it automatically on disks for which it’s appropriate), you might check to see if the disk is particularly fragmented by running the defrag tool. If your disk is low on space, it’s possible that the automated defragging isn’t able to properly complete its task.

How Should I Keep My Hard Drive Clean and Working at Its Best? has more tips and tricks on keeping your hard drive running smoothly.


Other software running on your machine can also slow things down. Having lots of other things running at the same time can have a negative impact.

The most common scenario is disk access. If your disk light is flashing continuously before you even start the copy, then something is already accessing the hard disk, which may slow everything down. Sometimes it’s hard to determine exactly what programs are accessing the hard disk, but I Have Constant Disk Activity and I Don’t Know Why. How Can I Tell What Program Is Doing It? may help.

The copy program itself can sometimes be at fault, in a way, if you’re low on RAM. Some copy programs work by first reading the entire file into memory and then writing the entire file to its destination. If your system is low on memory, that could be enough to cause the system to start swapping memory to disk, which in turn would interfere with the very copying operation you’re attempting to perform.

You can use Process Explorer to monitor your computer’s memory usage while you’re copying files to see if this might be the case.


Finally, we have to mention the various pieces of hardware involved when you’re copying files: the disk controller, the hard disk itself, the system board, interface(s) to the disk controller, USB interfaces and cables if it’s an external drive, and more. Typically, problems in these areas show up as slightly more severe than just a slowdown, but since you indicate that it also appears to hang, hardware issues might be something else to investigate.

Do this

As you can see, it’s difficult to say “Here’s your problem” because there are so many possibilities. Hopefully, one or more of the items I’ve mentioned will help resolve it.

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19 comments on “Why Does Copying Files Slow Down?”

  1. This is a tough one to solve without having hands on the machine.

    First I would check Event Viewer, under Administrative Tools in Control Panel. Always a good first step in troubleshooting a problem. If your hard drive is causing trouble, Windows will log errors there. Other errors may be relevant.

    It’s probably an application problem of some sort if the hardware checks out. Antivirus, antispyware and/or firewall applications seem to be the most common culprits of system problems.

    If you get a specific error message, rather than it just hanging there forever, hit Google for that error. Might find someone else with that problem and a resolution.

    I’d dig into it with Process Explorer and Process Monitor, but that’s well over the head of the average user.

  2. If I were you, I would see if I need additional memory. Ctrl+Alt+Del and then opening the “Performance” tab will show you available physical memory. If the available memory is LESS than the file you are trying to copy, or less than 75MB, I would into getting more memory.

    There are actually two types of memory:
    1. physical memory which is your memory stick (fast), and
    2. virtual memory, which is on the hard drive (slow).

    If your physical memory is full or close to full, windows will automatically “swap” data from your physical memory into a pagefile on your hard drive in order to free up physical space for later applications.

    This becomes a problem when you are flipping around multiple applications. Generically, your most frequently used applications (such as those in focus right now) will be moved to the faster physical memory instead of working on the hard drive. Flipping around from application to application will force data to be swapped back and forth multiple times if you do not have enough physical memory to hold everything you are working with at that moment.

    Also, performance wise (on systems limited by memory), it may be wise to only allow a single file to be copied at a time. Why? Memory will only need to be allocated to the size of just that specific file, and then cleared for the next file. Multiple MOVE instances will greatly increase the swapping to the hard drive.

    Also, generally, it makes no difference if you are moving 1 huge file or multiple small files, as long as you are moving 1 file at a time. Your CPU will only move data to memory on either a byte basis, word basis or long basis, every clock cycle, but it’s always the same amount of data at a time; nothing more, nothing less.

    For systems that have a lot of free memory, you will see the pagefile is much smaller and the system runs much smoother. It’s definitely worth it to get more memory, if you are using a lot.

    Also, check to make sure none of your applications are using a massive amount of memory. You can see this in the “Processes” Tab if you arrange by memory usage. > 100MB is a tell that something is wrong unless it’s a full screen application/game.

  3. If the copied file is going across a fast ethernet network router, check the NIC to see if its set at Full 100. If it is, try changing to AUTO. If at auto, try setting to FULL 100. One more thing. If you have multiple Spyware tools running, temporarily disable them all and try the copy again to see if that doesn’t solve it.

  4. Activities running at background pose a major problems especially if there are many virus guards(vgs) running at the same time. I saw in one laptop, AVG, Norton and AVIRA were actived. I dismissed the other two vgs and defragmented the hd. So everything is fine including downloading large files. One thing to take note, if the softwares were installed by the vendor then the problem already started. It is best to choose which software we need.

  5. One thing you didn’t say is what you’re copying from and to. If this is happening only when (say) you are downloading from your digital camera to your hard drive, but downloading large files fromm the internet or moving a big file from one directory to another on your hard drive go through just fine, then it’s very unlikely that it is a hard disk problem (or a system RAM problem, for that matter). Those sorts of problems would cause *everything* to choke. This is easy to check– just move a big file on your hard drive, download a couple of big files from different sites on the internet (at different times of the day, if possible), try copying to/from a USB device, etc.

    If it’s happening with just one (local) device, like your camera, then the first thing I would try would be to update (or reload) the drivers. I’d also check the manufacturer’s site for possible firmware upgrades, helper software, etc. for the device, plus possibly a FAQ page to address this issue.

    If it’s only happening from one web site, then I would suspect that the problem is on their end! Most service providers put bandwidth caps on their hosted sites, and also most sites are sharing resources with other uses– so a big demand on the server (not just the site itself) could also cause a huge slow-down or apparent jam-up on your computer. The only “solution” in this case is to be very patient (like start it downloading and then go to bed), or to try to download when the site volume will be low.

    If it happens from every internet site, but local copies work OK, then I’d look into a problem with your internet service. You could be sharing bandwidth on your internet connection with a surprisingly large chunk of your neighborhood, so if one of them has started doing bandwidth-intensive work when you commonly download your files, that could be a factor. (A friend of mine had this problem, and he found out that a radiologist moved in next door to him and was working from home.) Also, there could be some sort of degradation on your link– something as simple as water in a J-box could do it; and cables do, eventually, go bad. These are hard to troubleshoot without getting your hands on the hardware, though.

    Anyway, hope that helps. Good luck with your problem.

  6. I’ve also had this problem, particularly when copying large files 100 GB plus. (e.g. server backup files). One thing that really causes problems is if the destination drive is compressed, Windows just doesn’t seem to be able to cope and the copy just hangs after a while. The only solution seems to be to buy a bigger destination drive!

  7. Leo’s answer is wild pure speculation.

    Yes, good thoughts from Leo, but Janet hit the nail on the the head: the biggest piece of missing information is,

    “One thing you didn’t say is what you’re copying from and to.”

    I, too, kept asking myself, is a network involved? What is on the other side of the network? Is it Vista? What is the speed of
    the network? What else is the network doing?
    Is any compression involved? Any decryption?

    All of the answers are speculation, yours and mine included. My sense from the original question was that a network was not involved, but all the additional suggestions have been exactly what I was hoping for: more speculation and places to look.

    – Leo
  8. I’m wondering if the reader has multiple computers. If they do, then they can try copying a large file on another computer to find out if the problem exists across multiple computers? If it does, then the issue is most likely with the network or file server. If the issue is limited to one computer, I’d first open up the case and clean out the dust bunnies.

  9. Another issue relevant to the source and destination of the files. If the two are separate partitions of the same physical disk, then the process can slow down significantly due to the movement to and fro of the magnetic head that reads and writes from/to the surface of the disk.
    So if the slow-down appears when copying from another partition of the same physical disk but not from one physical disk to another then that is very likely the issue.
    Also, keep in mind that when two mediums with different transfer rates are used, the rate is determined by the slowest

  10. “SpinRite” might — or it might not — be a great product, BUT I checked out your “SpinRite” link, and quickly found one thing conspicuous by its absence. I’m extremely leery of people who don’t put the price of their product up front. Do a text search for a dollar sign (in MSIE, click “Edit” then “Find (on this page)…”, then type “$” without the quotes, and click “Find next”). Result? Nada! As soon as I see THAT on the homepage of a product, I quickly go looking for another product. It’s like with restaurants — if you actually have to ASK how much the bill is going to be, you can be sure you can’t afford to pay it! :(

    All I can say is that you must not buy much software online. I run into that all the time.

    For the record, as of this writing, Spinrite is $89 – less if you have an earlier version, and there’s site licensing available as well.

    To me, worth every penny.

    – Leo
  11. Try copying the files in SAFE (F5 boot) mode. This would be an easier test to see if the problem is with the operating system, hardware or competing software. Also test while temporarily disabling your anti virus software in Windows if the file copy in SAFE mode works OK.

  12. hello every one…..

    i give one solution try it…. and i am sure u will success… regarding this problem

    first copy data what ever….then pest in to another drive ..

    as data in d: drive then copy to e: or f: drive then after cut that data and pest in pen drive / another hdd

    u get maximum speed

    i hope u are happy.

    by the way have a good day.


  13. I noticed slowdown while copying to and from usb flash memory (or so) MANY + SMALL files! (e g you copy a whole site 3 G with many small files, gifs, js etc). It relates both to a new comp (Quad Intel, SATA HDD) and old (Pen 4, IDE HDD).

    My experiment in Win Xp SR1 was with TotalCommander (ver. 7 + up, go to they allow several possibilities in options : a/ small files + changes for buffer size; b/ big files c/ usb
    Outcome: regime a/ really much-much better if one copies manyyyy small files (I changed buffer size: “on the same disk” — 256, “on diff disks” — 128 [NB: I have plenty of RAM, 4 G]
    In case of big files (like CD/DVD or so) — just switch to b/ and determine the size of the buffer (I tried 10240 and resp. 64 — now it is really better).
    I also experimented with turning off Antiviruses (helps — if the source was clean).
    Speed is a bit higher in Linux.

  14. I too had the same problem, but only when I copied files from a CD. The process named “system” in my task manager would go to 99%. However, after formatting the C: drive everything is ok.

  15. OK..first off lemme say that this is a suggestion that all techs, even myself, immediately wish to dismiss out of their own pride of workmanship. So, with that said, let us all put that aside for this situation as it may help this poor user in a copying jam out.

    My suggestion is very simple. From my own experience I have found that this can be caused by a misaligned or bent pin that is not making contact within the data cable connection. Sounds like it would cause total failure but, it doesn’t always. I had a 160GB Seagate Barracuda IDE 7200RPM drive that would copy files VERY slow at times. Other times it would do ok but never at the speed it should’ve been. I also had other strange errors happen with DVD burners never wanting to work solidly. When trying to add another new HDD to the mix, I became extremely frustrated that none of the configurations were working no matter what drive got slaved or which one got set as master etc. Thinking it was my motherboard becoming a POC, I yanked out all the drives and when doing so realized that one little IDE/PATA pin on the Seagates interface was pressed completely flat. And I mean perfectly flat as though it happened at Seagate because if it had happened during install it would not have been so perfectly flat. I immediately set up an RMA return ticket and Seagate was happy to replace it. However, I being the always curious tech, got out a pair of my tech hemostats and gently pried the pin back into an upright position keeping it from breaking off. Plugged it back in gently and WHAM BANG! it’s been working with great xfer speeds ever since. Something that simple and easy to over look can cause this problem and many others as aforementioned. I canceled the RMA with Seagate and have been happily using the drive to this day with flawless performance. Seagates have never let me down, ever, and though this one probably left Seagate in it’s condition, it’s not letting me down now so, it’s a keeper as they say. Thanks and I hope that helps you and/or others who may be having the same strange unexplainable trouble(s). -SamusLife

  16. The only times I’ve had problems like this is after installing a new USB 2 PCI adapter. Sometimes the adapters are just bad but most of the time just changing the PCI slot corrects the problem.
    I’ve found that USB 2.0 PCI adapters can be very sensitive about which PCI slot they’re in as well as what PCI cards (sound, video, wireless, etc) are next to them.
    Good luck.

  17. I’ve always been annoyed at file copy code that does not show the actual copy progress. Most command line tools (copy/xcopy) just show you when the copy is completed. How can you tell if a copy is going slowly or if it is just hung? You can’t. Likewise with the (Pre-Windows 7) drag and drop. That is why for command line copying (again, pre-Windows 7) I used ROBOCOPY which is available free from Microsoft. It has scads of command line options (most of which you won’t need) including retry/wait counts. For example, to copy pdf files from c:\myfiles to d:\archive you could type

    robocopy c:\myfiles d:\archive *.pdf /r:5 /w:30

    /r says retry 5 times if there is a problem
    /w specifies 30 seconds between retries

    percent progress is displayed for each file

  18. In my case it was ethernet cable. Exactly, the pin was not pushed to the end of the Ethernet card. Chceck if your cable is wired like it should be, or try other cable… I was wondering what it is for two days, then one programmer told me it can be cable. Before I tried so many thing without luck :-) Now second day it seems everything is OK. Bye administrators ;-)


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