This procedure divides the existing partition in half, unless it's more than half full. Click on a pre-existing partition in the Volume Scheme list, and click on the '+' button. Subdivide an existing drive partition to reallocate its space without losing the data already on it. To format and partition a disk for use on a Windows PC, use Master Boot Record as your partition scheme. Select any partition that you plan to use as a startup disk for the Mac OS and click on the 'Options' button to set its partition as GUID. To alter partition sizes interactively, drag the dividers between them in the Volume Scheme list up or down.

Click on the listing for each partition in the Volume Scheme list and enter a name, format and size. Set a volume scheme using the drop-down menu of the same name, or use the '+' and '-' buttons below the Volume Scheme area to add or remove partitions from its list. If you clicked on a partition name instead of a volume name in the list, the tab won't appear. Even a drive you format as one unified piece of storage space contains a partition equal in size to the addressable size of the mechanism.Ĭlick on the 'Partition' tab at the top of the Disk Utility interface. Note that drive names appear flush left in the list, with the names of their partitions indented below them in alphabetical order. Look in the list on the left side of the Disk Utility interface for the name of the drive you want to partition, and click on the applicable listing.

Seagate format tool