I have been using several different embedded boards that store kernel, init files, filesystem, etc. on partitions of a (micro)SD card. I notice in the example usage or instructions that compressed image (zImage) is loaded to the corresponding partition of the SD card (let's say sda2).

I wonder if it would be fine to load uncompressed image file (Image) to the sda2.

If it is a fine case, would the board boot some seconds faster than the one that has zImage or the difference would be insignificant?

And, is there any specific reason to use zImage apart from saving storage space?

  • 2
    All of this is completely dependent on the bootloader. Commented May 17, 2013 at 16:31
  • Could you please elaborate how it depends on the bootloader?
    – sven
    Commented May 21, 2013 at 20:48
  • Kernel compression isn't supposed to depend on the bootloader. The kernel has its own decompression stub and the kernel is supposed to be jumped to in the same way whether it is compressed or no. Commented Mar 24, 2017 at 18:58

1 Answer 1


Try it. I did try CentOS with an uncompressed kernel and it works well with pygrub.

The almost historical reason for the compressed images is that they had to fit on a 1.44 MB Floppy.

Compression is still great if you do a network boot via low banbandwidth network.

  • Generally, once you have a fast enough CPU/memory combo, using compression is faster - decompressing is just quicker than loading the uncompressed image (for example using slow CF/SD card).
    – peterph
    Commented May 23, 2013 at 21:26

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