Difference Between Wic and Hddimg Format in Yocto

Difference between wic and hddimg format in yocto

There was not much info about online, so I asked this question in the intel community and here is the response of that:

Generally a .wic image is intended to be installed directly to its final destination, whereas an hddimg is for evaluation and installation elsewhere.

By default meta-intel .wic images only have an EFI bootloader, and will not boot via legacy BIOS.

An hddimg will have both an EFI bootloader and the syslinux binaries that let it boot from legacy BIOS.

On startup with your installer USB image do you get a light gray screen with four options? If so it is booting via legacy BIOS.

Yocto wic Creates Unexpected Small Partition

The mmcblk0p4 (1K) partition is an extended partition. When using a master boot record (MBR) to partition storage into more than 4 partitions one must use 3 primary partitions and 1 extended partition. This is because there is a maximum of 4 primary partitions. The extended partition may hold multiple logical partitions.

mmcblk0         <- Entire Storage
|--mmcblk0p1    <- Primary Partition 1
|--mmcblk0p2    <- Primary Partition 2
|--mmcblk0p3    <- Primary Partition 3
|--mmcblk0p4    <- Extended Partition
   |--mmcblk0p5 <- Logical Partition 1
   |--mmcblk0p6 <- Logical Partition 2

This is not Yocto specific. I use Buildroot and have a similar layout. The commonality is the disk partition method not the Linux distribution.

• Wikipedia: Disk Partitioning
• Serverfault: Primary vs extended partitions on Linux

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