Insyde BIOS Issues

Insyde is a relatively new UEFI-style BIOS manufacturer. Unfortunately their product, Insyde H2O, leaves a great deal to be desired in terms of code quality.

Insyde The Crashing BIOS

The Insyde BIOSes distributed on many laptops are liable to crash where an MBR-formatted hard disk contains a partition with contents in violation of Insyde H2O's expectations.

This is shocking and extraordinarily wrong for several reasons:

  • It Can Crash: Firstly and most obviously, the contents of the hard drive can crash the BIOS.
  • Premature Inspection, or “it reads partition contents before it even knows it needs to”: When I say “crash” here, I mean it; the BIOS crashes at the vendor logo. You cannot select to boot from an optical drive or other medium, because Insyde H2O does its inspection of the hard drive before processing user input, and thus before even knowing whether it's going to try and boot from the hard drive, it crashes. The only way to recover the computer is to remove the hard drive and boot without, or change the contents of the hard drive to be less allergenic to Insyde H2O.

When Insyde H2O boots and finds a disk, it inspects the first partition, no matter whether it is MBR or GPT formatted. I don't know whether Insyde H2O cares about the partition type code on MBR disks. Either way:

  • A FAT32 first partition on an MBR disk with type code 0x07 works.
  • A NTFS first partition on an MBR disk with type code 0x07 works.
  • An encrypted first partition on an MBR disk with type code 0x07 causes a crash.

Mercifully Insyde H2O appears only to care about the first partition it finds. The contents of subsequent partitions can be as random as they like.

The GPT disk partitioning scheme also has a per-partition flag bit (bit 1) for specifying that the firmware should not attempt to boot using the partition. Setting this bit would probably be an effective workaround for people using GPT-partitioned disks.

Model lines known to use Insyde H2O

  • Acer Aspire
  • Acer — most other laptops, apparently
  • HP Pavilion dv
  • HP Envy


2015-11-20: A commenter pointed out that the UEFI specification in fact allows UEFI BIOSes to perform UEFI boot from an EFI System Partition stored on an MBR-partitioned disk. Previously, the article erroneously assumed that UEFI BIOSes should not examine MBR partitions for the purposes of booting via UEFI, and that Insyde H2O's examination as such was in violation of the specification. In fact, this is both allowed and required by the specification.

2015-11-20: Updated article to note GPT firmware-ignore bit.