Why can’t I access my 4TB hard drive’s full capacity?

QI’ve upgraded my Windows 7 PC with a 4TB hard drive. My 1.5TB and 2TB drives already work, but I can only access 2.2TB of my new 4TB drive. All three are NTFS formatted, and I’ve checked the drive’s partition scheme. Can you help? Paul Finch

AWe think the 4TB drive is configured as a master boot record ( MBR) drive, which addresses sectors of the drive using 32bit numbers, giving a maximum of 232 sectors. Each has a capacity of 512 bytes, giving a rough total of 2.2TB.

You need to convert the drive to the GUID Partition Table ( GPT) format, which uses 64bit numbering. First, back up the drive, then use Disk Manager to delete its partitions and volumes until it shows only Unallocated. Right-click the ‘disk information’ tile (to the left of the bar where you deleted the partitions) and the GPT conversion should be available. Now you can re-create the partition(s) and copy your data back on.

But because your motherboard has a conventional BIOS, rather than the newer UEFI type, your PC won’t boot if you have Windows installed on the 4TB drive. You’ll need to install it on one of the other drives, or use cloning software to move the contents. This will overwrite what’s on the smaller drive, so back it up.

After doing this you probably can’t delete all the existing partitions on the 4TB drive and won’t be able to convert it to GPT. Solve this by running Diskpart in Command Prompt (the same tool we recommend Trevor Moore uses on page 65).

Type diskpart, press Enter, then type list disk and press Enter. Now type select disk X, where X is the number of your 4TB drive as displayed by list disk. When Diskpart confirms the drive has been selected, type clean, press Enter, and you should see ‘Diskpart succeeded in cleaning the disk’. Disk Manager should now show that the drive is empty and can be converted to GPT.