Microsoft Windows installation is nowadays mostly carried out using USB flash drives. This method is more convenient when compared to the traditional CD/DVD drive method. However, small number of users may still be using the traditional CD/DVD drives for installing windows due to its simplicity. In this article the focus is on preparing a bootable system using an external USB drives. However, the same rule will still apply if you are using a CD/DVD drive with a slight difference.

Modern systems have evolved in the way they boot the operating system and have increased in complexity. This guide aims to address the correct procedure to fix and avoid booting problems. To simplify the booting process options, we have developed a unique UEFI/MBR boot table that users can use as a reference guide when they encounter booting issues.

New BIOS standard, known as UEFI, was introduced in 2012. Windows 8 was the first version to utilise this new technology. This new method introduced new improvements to the traditional MBR based BIOS. Among these improvements are: Improved security, faster booting time, increased number of possible partitions and support for hard drives that are larger than 2TB.

For a successful UEFI BIOS booting many conditions must be satisfied:

  • 64-bit operating system.
  • GPT based hard drive partition.
  • Additional FAT32 partition for boot files.

In order to simplify the booting process, we have created a UEFI/MBR boot table as shown below. The area in green shows the conditions for a successful booting process, whereas the area shown in red displays a failed booting process. If you can match the settings of your hardware (motherboard), bootable USB/CD drive and internal hard drive, only then your system will boot correctly.

UEFI/MBR Reference Booting Table

The table above assumes the following possible combinations:

  • 2 hard drive formats (MBR, GPT).
  • 3 motherboard BIOS settings (legacy bios, legacy uefi, uefi).
  • 4 external USB drive settings (iso-uefi-fat32, iso-uefi-ntfs, iso-mbr-fat32, iso-mbr-ntfs).

So in theory there are a possible combinations of events totalling (2 x 3 x 4 = 24). These combinations are not set in stone and it is possible to expand it to include further variations such as; secure boot, NTFS, FAT32, etc. However, it is more practical to reduce the size of the compatibility reference boot table in order to make it more usable and decrease complexity.

The UEFI/MBR reference boot table includes some assumptions that have been made and referenced in the legends under the table. For example, the secure boot option setting may impact the success of the booting process. It is therefore recommended to disable this option during the installation process, and re-enable it after the completion of Windows installation.

In the legacy MBR format, hard drives can have NTFS/FAT32 format and boot files were stored inside the system hard drive, usually C drive. However, in the UEFI BIOS a FAT32 partition is required for storing the boot files. This is in addition to the standard system drive, which is usually NTFS formatted. Furthermore, for UEFI BIOS mode the hard drive must be initialised as GPT format.

Microsoft Windows installation media are now commonly used in bootable USB flash drives. The format of the installation files in the USB drive must also comply with the requirements in order to install windows successfully. However, you can assume that most modern ISO installation files are UEFI compatible. In comparison if you have Windows 7 then it may not be UEFI compatible therefore you need to adjust your BIOS settings and hard drive format accordingly.

To prepare a USB media for Microsoft Windows installation you need to use a special utility in order to make the USB drive bootable. The most common utility is provided by Microsoft and known as Windows Installation Media.  An alternative option is to use the Rufus utility as it has a very flexible approach. Unlike Microsoft tool, this utility has many options that can be configured to meet your requirements.

Hardware BIOS options also must have the correct settings to enable the system to boot. Usually the BIOS options are accessed by pressing a special function key such as F2 after powering up the system. The figure below shows a BIOS screen taken from a Dell computer. Modern systems commonly include four options for booting: Legacy MBR, Legacy UEFI, UEFI only and Secure Boot. Once again, these options must be aligned with the format of the internal hard drive and bootable media.

PC BIOS Boot Options

If you are using a bootable CD/DVD drive instead of a USB drive then the proposed Reference Boot Table will still applie. However, you may encounter improved compatibility when booting CD/DVD that contains UEFI files. This means CD/DVD that contains images based on UEFI format may still boot under both legacy or UEFI modes. If the CD only contains the standard MBR files then it will only boot under legacy settings.


Please observe the following for a successful booting process:

  1. Use the UEFI/MBR reference boot table to check if your settings are correct.
  2. MBR scheme should only be used with older systems or 32-bit OS versions.
  3. New computers should use the UEFI scheme where possible for the advantages mentioned earlier.
  4. Disable secure boot if you are using modified ISO files or having booting issues. Don’t forget to re-enable this option to secure you system.
  5. UEFI will only work with 64-bit systems.
  6. UEFI requires GPT based hard drive.
  7. UEFI stores boot file on a separate FAT32 partition.
  8. IF your bootable ISO image is UEFI based and contains a file that is larger than 4GB, then you will need two partitions inside your USB drive. First partition must be a FAT32 for storing boot files, and a standard NTFS partition for storing system files. There are utilities available such as Rufus that will automatically partition your USB drive to meet these requirements.
  9. If you are still using CD/DVD drive the MBR/UEFI reference boot table is still valid. However, depending on your hardware, you may find that it is a little more flexible with UEFI booting. For example, you may be able to boot a UEFI DVD using the legacy mode.
  10. The proposed boot table is also valid for any bootable software/utility and not just Microsoft Windows software.

Finally, if your system is already formatted and you change the BIOS options your system may not boot. Once again use the proposed boot table to check that all the set parameters are compatible. This procedure, if followed, will help you repair any system booting problem.