Sharing an external drive between a Mac and a PC under Tiger and earlier

This FAQ addresses two methods of sharing a an external drive, such as a FireWire® or USB 2.0 drive, between:

  • a Mac® running either Mac OS X 10.4 Tiger® or Mac OS X 10.3 Panther® and
  • a PC running Microsoft® Windows®.

It is based in part on information in our book, Troubleshooting Mac® OS X.

Two methods of sharing an external drive between a Mac and a PC are discussed:

Physically sharing an external drive

You would use this approach if you planned to use your external drive individually with a Mac or a PC, i.e. physically connected to one type of computer at a time. For example, you might have a Mac at home and a PC at work and want to move physically move large files between the two locations using a portable hard drive.

Since both Mac OS X and PCs can read and write to disks in MS DOS format, you can format the entire external drive in MS DOS format. However, there are some significant drawbacks to this approach:

  • Disk Utility only permits you to format the entire drive in MS DOS format: it does not permit you to partition the drive so that some partitions are in MS DOS format while others are in Mac OS Extended (aka HFS Plus or HFS+) format.
  • When you copy or save a file from a Mac to a Windows shared volume or Windows-formatted disk, the Mac creates two files:
    • the data fork (xxx), and
    • the resource fork (._xxx)
  • where xxx is the file name. This is called Apple Double Format and is normal. The resource fork contains metadata about the file that is exclusive to the Mac. This is new with OS X, as documented in "Mac OS X: Apple Double Format Creates File Name With the Prefix '._'."
  • Serious problems can arise if you move the file (xxx) separately from its resource fork (._xxx) on the PC and then try to open the file on the Mac.
  • If you plan to work with large files, such as digital video, the largest file you can write to a disk in MS DOS format is 4GB. The MS DOS format is also known as FAT32.
  • If you connect an MS DOS-formatted disk larger than 128Gb to a Mac running Jaguar, the disk will not show up in Finder. See "Mac OS X 10.2: MS-DOS Disk Does Not Appear in Finder."

To avoid these problems, we recommend you format the external drive in Mac OS Extended format and install Mediafour™ MacDrive™ for Windows on the PC. MacDrive for Windows is probably the state-of-the-art application for enabling you to use Mac-formatted disks and hard drives on Windows-based PCs.

Sharing an external drive over a network

If your Mac and PC are on the same local network, you can format the external drive in Mac OS Extended format, connect it to your Mac, then share it over your network with the PC. This beats "sneaker-netting" the drive between two computers on the same network.

The easiest way to share your Mac's external drive with your PC is to use the donationware application SharePoints. Be sure to review the following FAQs on their Web site:

You will also want to review and implement the instructions in the following Mac Help and AppleCare® Knowledge Base documents addressing file sharing:

Finally, note that with Mac OS X file sharing, only Public folders are shared by default. However, you can share more by logging in to the Mac from the PC with an Admin account on the Mac. See "Mac OS X: How to Share More Than Public Folders."

Support for SharePoints can be obtained via the SharePoints Forum.

Did you find this FAQ helpful? You will find a wealth of additional advice for preventing or resolving Mac OS X problems in Dr. Smoke's book, Troubleshooting Mac® OS X.
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