6 Replies Latest reply: Aug 10, 2010 10:44 PM by aoz8080
Gerard James Level 1 Level 1 (5 points)
I've got a new 27-Inch iMac 2.66GHz Intel Core i5 with 4 GB RAM, less than a month old. I'm noticing that I'm getting slow file transfers on two (out of four) of my USB 2 ports. I've tried two different hard drives and a USB flash memory stick and the files seem to copy very slowly sometimes. Is there a known problem with the USB ports on these new iMacs or is there a way to fix this? I've tried using the other two USB ports for my backup hard drives which seems to solve the problem so I'm wondering if I don't have a couple of bad ports? The files will still copy okay to the ports in question but they are slower to copy as opposed to the ports that "work" better. I'm wondering how to tell if a USB port is actually "bad", would the file transfers work at all if this were the case or would I just get slow throughput? Is there a utility that can test the ports?

Thanks in advance.

27-Inch iMac 2.66GHz Intel Core i5 - 4 GB RAM, Mac OS X (10.6.2), Other Macs: Power Mac G5/Dual 1.8GHz Running Mac OS X 10.4.11
  • Nik Carrier Level 1 Level 1 (5 points)
    I am in a similar situation to you. I have a 27" i5 less than a month old and have noticed USB issues. It took me almost 2 days to restore my iPod...I assume because of the same issue as you. Which 2 ports were working correctly? I would like to try to use them.

    Strangely, one of these ports seemed to corrupt my iPod. It began to act strangely shortly after syncing to my new mac. Restored, problems got worse..tried to reformat using disk utility and the iMac 27" was unable to format, tried several times, repartitioning, repairing, reformatting...I thought my iPod might be dying. On a whim I decided to try to fix it on my macbook instead, and boom it erased and restored quickly and perfectly.. I am a little concerned how to prove this problem to tech support if I require a repair. I will see if problems begin to occur again
  • derektom Level 1 Level 1 (0 points)
    Hi Gerard,

    Which are the slow ports for you?

    I've got an i7 iMac 27" with 8GB RAM and running Mac 10.6.2. I have a 888GB Seagate FreeAgent Go USB hard disk attached to it. I have tried with the hard disk connected to the 2 USB ports closest to the right side (facing the front of the Mac).

    Interestingly, copying files in a Windows XP virtual machine (VMWare Fusion 3.x) with 3GB of RAM allocated is about twice as fast as when copying directly in Mac OS X. I need to point out that the disk is formatted in NTFS but I am running the latest Paragon NTFS for Mac 8.0 (commercial NTFS driver for Mac).

    Mac OS X 10.6.2
    15 mins 50 secs

    Windows XP virtual machine on same machine with only 3MB RAM allocated
    8 mins 7 secs

    I believe from my results above and reading about this problem from others in Apple Discussions, USB file transfers are abnormally slow on Core i5/i7-powered Macs.
  • Lanternfly Level 1 Level 1 (0 points)
    I have a new 27" i7 with 8 GB of RAM. If I connect my keyboard to port 1&3, the boot up time is 30 secs. If the same keyboard is connected to either port 2 or 4, the boot up time is 3 minutes. Port 1 is closest to the earphone port & port #4 is next to the firewire 800 port.
    In my opinion, there is a problem with the USB ports on this model as they do not function equally and 2 of 4 slow the machine down dramatically with the keyboard attached when booting up.
    A product specialist spoke with an Apple engineer re this & the engineer said the ports do function differently and this was normal. I do not agree that this is either normal or acceptable. There is a flaw in either the hardware or the software or both.
  • den.thed Level 7 Level 7 (24,720 points)
    Hi Gerard and others;

    Some early build versions of 10.6 had issue's with MS-DOS FAT-32 formatted USB External HD's.

    Download and install the 10.6.3 Combo Update > http://support.apple.com/kb/DL1017

  • lpfuria Level 1 Level 1 (0 points)
    Hi all.

    My brother and I have each one an iMac 27 i5 at home. We note the reported problem of the USB ports. The ports which belongs to the USB connecting the built-in isight (assumed 1-3) are faster. The others are slow.

    Copying large files to external USB hard drive through the faster ports we get 30mb/s for the slower we get 20 MB/s.

    However when we connect another device sharing the ports 1-3 speed drops. Oddly varies the falling rate. For example, when connect another hd falls to 25mb/s, when connecting an iPhone dropped to 20mbs/s…

    I think it's a hardware problem. Don't know. Don't like it! Sorry poor english.
  • aoz8080 Level 1 Level 1 (0 points)
    I have noticed the exact same problem on two different iMac 27" i7's. I think it's an unfortunate result of internal devices sharing the USB host controllers.

    The "fast" ports are indeed 1 & 3 (#1 being the outermost, next to the audio ports). With either of these I can read large files from an external HFS+ HDD at a steady 36MB/s, provided that only one of those ports is being used. With ports 2 & 4 (#4 being next to the firewire 800 port) I get half that rate, i.e. 18MB/s, again with nothing in the other port of the pair.

    I also have a late 2008 MacBook Pro 15" with just two ports, but they are both fast at 36MB/s, even if you have something plugged into both of them. That's about as fast as you get for USB 2.0 in the real world.

    My solution is to use #2 & #4 for slow devices like keyboard and mouse, and use #1 for the HDD and keep #3 empty (actually I plug my UPS into #3 since that particular device doesn't slow the HDD much, just down to 34MB/s).

    *Your best bet though as always is to use FireWire 800!* I get 80 to 85MB/s on that (FireWire is just more efficient than USB 2.0, as well as being clocked faster).