How do I format external HDD so it can read/write?

Format it as MS-Dos (FAT) using the program Disk Utility.
Both windows and mach can read FAT.

The following is from the help function in disk utility:
NOTICE:Formatting a disk erases its files. Copy files you want to save to another disk before formatting the disk.

To format a disk for Windows computers:

In Disk Utility, select the disk you want to format for Windows computers.

Click Erase, and choose MS-DOS (FAT) from the Format pop-up menu.

Type a name for the disk.

The name’s maximum length is 11 characters.

Click the Erase button, and then click Erase again.

 

thats just gay tbh, FAT32 is useless these days, it can only handle files below 4GB..

if you wanna use files larger then 4GB you will have to install software on either machine.

if you want to use NTFS - the faildows format - you can install paragon NTFS 8.0 to enable write access from the mac (it can already read NTFS)
if you want to use the mac format HFS+ you can install macdrive on the faildows machine to enable it to read and write to HFS+.

both these formats support files up to 16 EB (and yes i men EB), the hard drive capasity is however usually limited to 2TB by the disk hardware, but then again most people don't have 2TB disks yet.

 

FAT32

• Read/Write FAT32 from both native Windows and native Mac OS X.
• No individual file larger than 4GB.

NTFS

• Read/Write NTFS from native Windows.
• Read only NTFS from native Mac OS X
• To Read/Write NTFS from Leopard: Install MacFUSE and NTFS-3G. You can install both with NTFS-3G for Mac OS X.
• To Read/Write NTFS from Snow Leopard: Guide: Enable native NTFS Read/Write in Snow Leopard
• (Be aware that some are of the opinion that enabling native NTFS in SL is unstable/unreliable, and favor the MacFuse/NTFS-3G method for Snow Leopard)

HFS

• Read/Write HFS from native Mac OS X
• To Read/Write HFS from Windows, Install MacDrive
• To Read HFS (but not Write) from Windows, Install HFSExplorer

 

You don't have to install Windows on your Mac. Read my post about NTFS, follow those instructions, then you can format the drive as NTFS from your Mac.

 

Correct, as Windows reads/writes NTFS natively, as my post stated.

 

As Windows is able to write and read NTFS formatted volumes, and read and write to FAT32 formatted volumes, there is no need to install additional software on Windows.

NTFS-3G only is meant for Mac OS X, to be able to write to NTFS formatted volumes.

 

No, you enable NTFS or install NTFS-3G on your Mac. Then you can format the drive using Disk Utility. Until you enable NTFS or install NTFS-3G, Disk Utility doesn't show NTFS as a formatting option.

 

Don't use the Erase option.

1. In Disk Utility, select the drive (where it shows the drive capacity)
2. Click the Partition tab.
3. Select 1 Partition as the Volume Scheme
4. Select NTFS
5. Click Apply

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