MBR can only have partitions up to 2TB and a maximum of 4 primary partitions per drive. You can have more if they are logical partitions. So it should be ok with a 1.5TB drive. GPT is new and only supported by some BIOSes, Windows Server 2003, Windows Vista and presumably Windows 7. Maximum partition size is 256TB and number of partitions is 128. Sound like something for the future. More info about GPT http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx