External storage question??

You can create two partitions on the drive, with a different format for each partition. Also, OS X can be made to read and write to NTFS, just as Windows can be made to read and write to HFS+. Yes, you can use the HFS+ partition for Time Machine backups.

Format A Hard Drive Using Disk Utility (which is in your /Applications/Utilities folder)

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Choose the appropriate format:

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HFS+ (Hierarchical File System, a.k.a. Mac OS Extended (Journaled) Don't use case-sensitive)

• Read/Write HFS+ from native Mac OS X
• Required for Time Machine or Carbon Copy Cloner or SuperDuper! backups of Mac OS X system files. [*]To Read/Write HFS+ from Windows, Install MacDrive [*]To Read HFS+ (but not Write) from Windows, Install HFSExplorer
• Maximum file size: 8EiB
• Maximum volume size: 8EiB
• Mac OS X: Mac OS Extended format (HFS Plus) volume and file limits
• You can use this format if you only use the drive with Mac OS X, or use it for backups of your Mac OS X internal drive, or if you only share it with one Windows PC (with MacDrive installed on the PC)

NTFS (Windows NT File System)

• Read/Write NTFS from native Windows.
• Read only NTFS from native Mac OS X [*]To Read/Write/Format NTFS from Mac OS X, here are some alternatives:
  • For Mac OS X 10.4 or later (32 or 64-bit), install Paragon (approx $20) (Best Choice for Lion and later)
  • For 32-bit Mac OS X, install NTFS-3G for Mac OS X (free) (does not work in 64-bit mode)
  • For 64-bit Snow Leopard, read this: MacFUSE for 64-bit Snow Leopard
  • Some have reported problems using Tuxera (approx $36).
  • Native NTFS support can be enabled in Snow Leopard and Lion, but is not advisable, due to instability.
• AirPort Extreme (802.11n) and Time Capsule do not support NTFS
• Maximum file size: 16 TB
• Maximum volume size: 256TB
• You can use this format if you routinely share a drive with multiple Windows systems.

exFAT (FAT64)

• Supported in Mac OS X only in 10.6.5 or later.
• Not all Windows versions support exFAT. See disadvantages.
• exFAT (Extended File Allocation Table)
• AirPort Extreme (802.11n) and Time Capsule do not support exFAT
• Maximum file size: 16 EiB
• Maximum volume size: 64 ZiB
• You can use this format if it is supported by all computers with which you intend to share the drive. See "disadvantages" for details.

FAT32 (File Allocation Table)

• Read/Write FAT32 from both native Windows and native Mac OS X. [*]Maximum file size: 4GB.
• Maximum volume size: 2TB
• You can use this format if you share the drive between Mac OS X and Windows computers and have no files larger than 4GB.