GPT (GUID Partition Table) is a partition type for disks. When formatting Mac-formatted disks, such as HFS+ or HFS+J, in Disk Utility, current versions of the Mac OS typically use GPT as the default partition type.
MacDrive fully supports GPT partitioning for fixed disks. Fixed disks can include internal hard drives, but can also include portable devices such as external hard drives which connect via USB, FireWire, etc.
No additional software is needed to access a Mac-formatted disk that is GPT partitioned. You can simply connect the disk to your computer, and MacDrive will be able to access the disk and assign it a drive letter.
Removable devices, such as flash drives or SD cards, cannot be GPT partitioned and work with MacDrive. This is because Windows does not currently support GPT removable devices of any kind, including those formatted NTFS, the most common Windows disk formatting type. A removable device can be identified as it will appear in the "Devices with Removable Storage" area of when viewing available drives ('Computer' in Windows 7/Vista, 'This PC' in Windows 8). The only exception to this rule about GPT removable devices is Windows XP, which didn't have this limitation; Microsoft added it in Windows Vista and later.
MacDrive does, however, support Mac-formatted removables with the partition types of APM (Apple Partition Map) or MBR (Master Boot Record) to get around this Windows limitation, either of which can be created with Disk Utility.
To create a removable drive that will work with MacDrive, you can use either Disk Utility or the MacDrive Disk Manager. Please make sure to migrate any data from the device as repartitioning it will erase all data.
Open Disk Utility by opening "Applications" from the Dock, and then "Utilities". Then, select Disk Utility. Connect the removable device in the left panel. Then, select "Partition".
Select the drop-down under "Volume Scheme" to select the number of partitions you want (usually, one). Then, select the "Options" button and select an alternate partition scheme, such as Apple Partition Map. Then, press OK, then Apply. You will be asked to confirm the change; press Partition to proceed.
MacDrive Disk Manager
Connect the device in question, then open "Computer" or "My Computer" to view connected devices. Right-click on the removable device and select "Format Mac Disk", then select "Modify Mac Volumes". Select the device, and press "Format Volume", then Format. The result will be a Mac-formatted removable device that can freely be used on Macs, or in Windows with MacDrive.