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Partition your USB disk (10.4)

External hard disk drives that plug into the USB or FireWire socket are becoming increasingly cheaper and bigger, making them one of the most popular add-ons. With capacities of up to 1Tb (1,000Gb) available, what should you do with all that space? Simply using all the space as a single hard disk drive isn't always the best way to use it and partitioning the drive has many benefits.

When a disk is partitioned, the space is split into two or more smaller chunks. For example, a 500Gb disk could be split into two 250Gb partitions, or 2 x 200Gb and 1 x 100Gb partitions. Each partition will act like a separate hard disk drive and each one appears as a separate disk drive in Finder instead of one.

The benefit is that one partition could be used for system backups and another for digital media, like video clips. You can use different partitions for different purposes, but this isn't the only benefit and an error in one partition will quite often only affect that partition and the data stored on the other partitions is often OK. (It's not always true, but most faults are software related rather than hardware and software faults are cured by formatting the partition.)

So how do you partition a disk? Go to the Applications folder, open the Utilities folder and run Disk Utility. All the disks are listed on the left and you can select the external USB disk to view its details. Select Partition at the top and you'll see the single large partition displayed.

Mac Disk Utility

Click Split and the disk space is divided into two. They don't have to be equal and you can enter their sizes into the Size box. You can select the format too and MS-DOS is available if you want to use the disk on a PC as well as a Mac, otherwise Mac OS Extended is best. The Options button at the bottom enables you to choose different partition schemes and you can allow a Mac to boot from an external disk or not (it's really your choice).

Once you have chosen the number of partitions and their sizes, click Partition to complete the job. You can then quit Disk Utility and the partitions will appear as disk icons on the desktop.

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