Change mbr partation to gpt

Question

I already have install ubuntu and now i want to insatll windows 8.1 over it. But while doing this this shows the problem that you should have gpt partaion. So i have to make this parataion from ubuntu but couldn't. So please help me

Answer 1

You're headed down the wrong path. Fundamentally, you need to understand that most modern computers support two entirely different and incompatible ways of booting:

• BIOS mode -- This is the old method of booting, which uses (typically) the Master Boot Record (MBR) partitioning system and boot code that's stored in the first sector of the disk (aka the MBR). Old computers used BIOSes, but new ones support this mode through a feature called the Compatibility Support Module (CSM), aka "legacy mode support" or a similar term.
• EFI mode -- This is the new method of booting, which typically uses a GUID Partition Table (GPT) on the disk and boot code stored as a file in the EFI System Partition (ESP). The EFI is a replacement for the BIOS, but many people and manufacturers continue to use the term "BIOS" in reference to EFIs, which is misleading. Also, know that the Unified EFI (UEFI) is EFI version 2.x; most new computers are actually UEFI-based, but Macs continue to use EFI 1.1.

Based on your symptoms, it sounds like you've got Linux installed in BIOS mode, but you've booted your Windows installation medium in EFI mode, so it's complaining that the disk uses MBR rather than GPT. (Note that MBR and GPT are both systems for partitioning the entire disk, so all the disk's partitions will be MBR or all will be GPT.) The solution to this problem is to figure out how to get the Windows installation disk to boot in BIOS/CSM/legacy mode. Forcing one boot mode or another can be tricky, and details vary from one computer to another. Typically, you'll need to enter the computer's built-in boot manager and select the entry for the boot medium that does not include the string "UEFI."

An alternative to this would be to convert from MBR to GPT partitioning by using gdisk on the disk, install Windows in EFI mode, and then install an EFI-mode boot loader for Linux. This approach has the advantage that it's usually possible to disable the CSM in an EFI, which simplifies the boot process; however, it will be more work up front to do all this.