What is exactly "Arch Fallback" in the Arch boot menu?
The Arch Wiki mkinitcpio page explains the difference between the two:
The fallback image utilizes the same configuration file as the default image, except the autodetect hook is skipped during creation, thus including a full range of modules. The autodetect hook detects required modules and tailors the image for specific hardware, shrinking the initramfs.
You can create your own image by using the
-g options to
mkinitcpio - this is helpful if you want to test your own images (to, for example, remove uneeded hooks), like so:
sudo mkinitcpio -c /etc/mkinitcpio.conf.new -g /boot/linux-new.img
From this post in the Arch Linux forum (edited for readability):
1) The kernel on arch is just one (i.e. there's no fallback kernel)
2) What's 'fallback' is the initramfs (the stuff that loads just after the kernel when you boot)
3) The difference is that the "normal" initramfs contains only the stuff that you configured to be there (
/etc/mkinitcpio.conf) and the "fallback" contains the default selection of drivers (eg all filesystem drivers, etc..)
So (as noted in a comment) it's an initramfs that loads everything. The kernel is the same.