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GUID Partition Table – GPT
Since the MBR partitioning scheme only allows a maximum drive size limit of 2.2TB and four partitions GPT (among other reasons) was developed. The new GPT supports a default of 128 partitions, has a built-in backup of the data structure and can handle disks up to 9.4 billion TB in size.
BIOS companies and PC manufacturers are moving towards updates and new hardware that support UEFI and boot to GPT partitions. You see, not only do you need BIOS that supports UEFI, you also need a GPT partitioned drive WITH an operating system that supports GPT booting. You are all probably running systems that have drives and BIOS that are MBR. GPT has been supported by Microsoft since 2002 but will only work on 64-bit Windows systems (except XP 64-bit) and not on 32-bit systems. Your current 64-bit default Windows 7 installations will be MBR.
Eventually 3TB will be inexpensive and available as the primary hard drives on PCs!
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UEFI and the GPT Boot
So how does GPT boot? The GPT incorporates a protective MBR that tells the BIOS it is a 2TB or smaller disk when you power on and lets the BIOS start the boot loader without issues. It does this so the low-level utilities can see the drive. This of course will only work if both the OS and the boot loader are EFI aware. EFI comes with its own boot loader so you can boot from a GPT.
Only certain equipment supports UEFI currently. A few current motherboards that support UEFI are HP EliteBooks, higher-end Dell PowerEdge servers and a few of the DP and DG Intel motherboards.
Check first with the vendor as they do not guarantee that list.
My HP EliteBook at work supports UEFI Boot Mode although my IT department uses MBR and 32-bit Windows. Bummer!
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Current Options for Large Drives
AMI (American Megatrends) talks about some options for workarounds to the current MBR/GPT issues.
- Install Windows on a drive smaller than 2TB with MBR. Use the 2TB or larger drives internally and have them partitioned as GPT.
- Use a BIOS (like AMI Aptio) and an operating system that support UEFI and allows GPT boot. You will need to get a UEFI OS installation disk
If you want to get a large drive and use it in your existing system you can just install it as a secondary drive. Western Digital has a great list of supported operating systems.
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Large External Disks and MBR
So, what about external drives? GPT cannot be used on removable media or on disks that are not connected to the buses used by the Cluster service. All external drives are MBR drives. The external drives from companies such as Western Digital and Seagate report 4K sector drives so the MBR can work with the lower number of sectors. Of course this can cause issues with home servers and older systems so check ahead before purchasing a large drive.
You can use 3TB drives as external drives when they are packaged from Seagate or Western Digital as long as you check compatibility with your system first.
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WD Caviar Green Drives – 2.5TB and 3TB
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These new drives are shipping with a Host Bus Adapter (HBA) that connects to an available PCI-E slot that allows the drive to work. This is a short-term solution since there are driver issues. This is what WD says, and I quote:
“If the large capacity drive is attached directly to the native motherboard SATA controller, the 3rd party driver may attach to the drive and the driver will not recognize the drive’s full capacity, resulting in an incompatibility issue. An attempt to uninstall the driver could render the whole system inoperable. However, when the drive is connected to the WD-bundled HBA, a Windows operating system would load native AHCI drivers that would correctly support large capacity drives and allow normal partitioning and use of the drive.”
I would suggest doing the research ahead of time on your system. I know for me, I will be buying one of these drives soon, but using it as a secondary drive and not an OS drive until I can figure out UEFI. I need to get a Windows 7 machine working with GPT before I spend the big bucks on a 3TB drive for testing!
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UEFI and Windows 7
I have already purchased an UEFI supported Intel motherboard and have been working on completing a UEFI installation of Windows 7. We decided to format a 300GB drive as GPT. If we are successful on the installation in UEFI then it will not matter what size the drive is as long as we format it GPT.
This is a great start for anyone wanting to learn the technical details of UEFI. The article is a Word doc on the right side of the page.
http://www.microsoft.com/whdc/system/platform/firmware/uefi_windows.mspx
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Converting from MBR to GPT
To change a disk from MBR to GPT you can use DISKPART in the command line or use the Windows interface. You have delete any volumes on the disk so this is NOT something you want to try until you need to perform the change. Again, this will not work on external attached drives and should not be done unless you need to do it.
You cannot convert your system drive or external drives to GPT.
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Main 600T UEFI Build Components
Michael Martis stopped by the house last week (10-30-2010) to help me assemble my UEFI test PC. The assembly was smooth and we formatted the WD drive in GPT on another machine ahead of time.
- Intel Core 2 Quad Processor Q8200 – $99
- Intel DP43BF Motherboard – $85
- Corsair 600T Case – $160
- Corsair H50 Liquid Cooler – $65
- XMS3 Dual Channel Memory – $40
- Corsair 400W PSU – $20
- Western Digital VelociRaptor WD3000HLFS 300GB – $140
- Video Card (Used, temporary card)
- Misc cables, DVD and Blu-ray – $90
The whole build (to be published in detail later) cost me $699. Not too bad.
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UEFI Installation Failure
I am not going to go into detail in this article today, but we could NOT get the system to install on a GPT partition. We have not given up though. It CAN be done! I will publish the results as soon as we get it running.
We plan on using a modified Windows 7 installation made with the Windows® Automated Installation Kit (AIK) for Windows® 7 as instructed by a member of Microsoft Answer named Samuel Tai.
Let’s hope Sam knows his stuff!
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Once I get the UEFI Windows 7 build complete and running I will publish a full article on the process.
I hope this gets you excited and interested in UEFI. It is our future.
See you soon. I hope…
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Tim
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