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I recently bought a Seagate for Mac 1 TB external hard drive. When I connect to my MacBook through the FireWire it works fine, but I also have media on my Dell laptop which is running Windows Vista. When I connect the hard drive to that laptop using the usb cable Windows doesn't recognize it. What am I doing wrong?

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is the drive still connected to the Mac's Firewire when you connect it to the Dell via USB? don't do that. –  quack quixote Apr 7 '10 at 20:58
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5 Answers

Its is probably the format of the drive. In general, Macs will read Windows formatted drives (FAT and, I believe NTFS), but Windows doesn't recognize Mac formatted drives (HFS+).

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The Mac will recognize NTFS but will not write to it. It will read and write to FAT32. –  emgee Apr 7 '10 at 20:57
mac can write to NTFS with ntfs-3g or other 3rd-party software. –  quack quixote Apr 7 '10 at 20:59
Yes, but not by default. –  emgee Apr 7 '10 at 21:36
@emgee: which is why i mentioned 3rd-party .. –  quack quixote Apr 8 '10 at 1:58
This may have changed since I dallied with it about a year and a half ago but I found that the 3rd-party solutions for writing to NTFS on a Mac have a tendency to corrupt/damage data on the disk. –  Nathan Taylor Apr 8 '10 at 1:59
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If you open the Disk Utility application on your Mac with the disk connected, you should be able to see it in the list of disks on the left hand column of the Disk Utility window.

If you click on the the partition (i.e. the name you see in your file tree when the disk mounts under OS X) what do you see for the Format at the bottom of the window?

If it is Mac OS Extended or a something similar then your disk is using the HFS+ file system, which is the default for OS X. This file system type is not natively supported by Windows, which is why the disk will not mount when you plug it into your laptop.

You have a couple of options:

  1. Reformat the disk to FAT32, which (as suggested by Michael Sturm) is the lowest common denominator in file systems between OS X and Windows. In addition to limitation to file sizes < 4 GB, you also lose a lot of nice features on HFS+ such as permissions and journalling.

  2. Create a FAT32 partition on the disk along side the existing HFS+ partition. This could be used to move data between the Mac and the Windows machine, but would suffer from all the same FAT32 issues mentioned above.

  3. Look at additional software which will allow for either NTFS or HFS+ to be read on OS X and Windows respectively. On the Mac, this can be accomplished using add-ons related to the MacFuse project. You should choose the filesystem that you plan on using most frequently so that it is as fast as possible and then reformat the disk accordingly. Using additional software like this will probably create a performance hit, but how noticeable it is depends on your usage pattern.

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This is most likely related to the used File System as Windows cannot use HFS+ (the Mac file system), Mac can not use NTFS (as far as I know) and the lowest common denominator - FAT32 - is not available as an option in the Windows Format Dialog (although I think there are tools to use it as it supports 2 TB Partitions).

File Size on FAT32 is limited to 4 GB though, disqualifying it for video applications.

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FAT32 is your best bet for compatibility. You may have luck with NTFS if you are willing to search a bit. –  Chris Nava Apr 7 '10 at 23:44
A good exmaple of where you might use files bigger than 4gb are disk image files. (.iso .dmg .cdr) –  Troggy Sep 7 '10 at 20:50
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Depends on the filesystem type and partitioning scheme whether it'll work on both. If the hard drive were formatted for HFS it would not show up on the Windows Computer. If the Partition Scheme were Apple Partition Map, it would also not show up.

For maximum compatibility, back up everything from the external hard drive onto your Mac. Open Disk Utility, select the external hard drive and go to Partition. Under Volume Scheme, choose 1 Partition, then click Options. Choose Master Boot Record. Click Ok. Then choose MSDOS under the Format menu. Then click Apply.

Your hard drive should work on either computer at that point, as well as others you may try to use it on.

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why do you have to do all that. Why wouldnt they make it compatible out of the box? Will I lose the fire wire performance on the mac side if I do that? –  Nick LaMarca Apr 7 '10 at 21:04
I think you'd be hard pressed to notice a change in speed. FAT32 does not have comprehensive permissions built into the file system, and I believe it less efficient when it comes to disk usage than NTFS. Note: you can see how a the drive is formatted by highlighting it in OS X and giving it a Cmd-i. It'll list it under Format. –  emgee Apr 7 '10 at 21:39
This is bad advice. Both Vista and Mac OS X can work with the more modern GUID Partition Table (GPT) partition map format as opposed to MBR. Intel Macs can only boot from GPT drives that have an HFS+ volume. So by formatting it MBR + FAT you'd be limiting it to being a very poor lowest-common-denominator drive that the Mac can't boot from. –  Spiff Apr 8 '10 at 0:37
This isn't bad advice, it's a trade-off situation. Simplicity vs. maximum compatibility. –  emgee Apr 8 '10 at 4:56
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If you want something that both machines / OSes can read a write, and that can act as an emergency boot drive for either machine, do this:

  • Reformat the drive, using the GUID Partition Table (GPT) as the low-level partition table format. Avoid Master Boot Record, which Intel Macs can't boot from. Also avoid Apple Partition Map, which Windows machines would have no clue about.
  • Give the drive one HFS+J (Mac OS Extended, Journaled) partition large enough to install Mac OS X onto (10GB+). This volume format accommodates Mac OS X and Mac files the best.
  • Give the drive one FAT32 (MS-DOS) partition, which both Mac OS X and Windows can read and write. This is a good place to put files that you want both Mac and Windows to have read/write access to. The FAT volume format is showing its age, but a huge variety of OSes know how to work with it.
  • If you want the drive to have a volume that's more optimal for Windows than FAT, give it an NTFS partition as well. This would be a good volume to install Windows onto, but beware that Mac OS X only has read-only support for NTFS built-in. If you want your Mac to be able to write to this partition, you'll need third-party software to enable this on Mac OS X.
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And you don't think this is overly complex for the op? –  emgee Apr 8 '10 at 4:56
@emgee This is Superuser.com, a site by and for computer enthusiasts, is it not? I like to assume the best of my nerd bretheren. –  Spiff Apr 28 '10 at 18:02
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