If you are confused by the many different firmware types and extensions in the LEDE firmware downloads table, read on, this pages tries to explain a bit about this topic.
You can help to improve this page by adding explanations for the different firmware types below.
See also imageformats and merge both pages into one.
|orion||not supported||not supported|
|sunxi|| ext4-sdcard.img.gz |
An initramfs and initrd are basically the same. It’s a filesystem in memory, which contains userland software. In an embedded environment it might contain the whole distro, on bigger systems it can contain tools&scripts to assemble&mount raid arrays and stuff like that before passing userland boot to them. Both can have a uHeader, to let uBoot know what it is.
The initramfs-kernel image is used for development or special situations as a one-time boot as a stepping stone toward installing the regular sysupgrade version. Since the initramfs version runs entirely from RAM, it does not store any settings in flash, so it is not suitable for operational use.
There are basically two potential reasons why only a sysupgrade image is available for your router, either the router is already running some kind of OpenWrt fork (which understands the sysupgrade format natively) or there simply is no known way to assemble a factory image accepted by the router.
uImage is (in most cases) a zImage with a 64 byte uImage header, which contains the load address & entry point of the zImage, so that uBoot knows what to do with it. Further is contains a description of the actual contents (linux kernel, version, …)
zImage is a compressed plain kernel with a ‘pyggyback’. Some extra code which can decompress the kernel before booting it.