See comments below:
> I intend to try Arch Linux in a MBR system (already running Windows and
> Linux Mint). It's wiki states:
> Warning: GRUB strongly discourages installation to a partition boot sector
> or a partitionless disk as GRUB Legacy or Syslinux does. This setup is
> prone to breakage, especially during updates, and is not supported by the
> Arch developers.
> https://wiki.archlinux.org/index.php/GR ... nless_disk
> I've come across this before in installing other Linuxes (Ubuntu,Mint) and
> ignored it. Sometimes (but not recently) GRUB gets updated and screws up
> BIBM in the MBR, and then I follow the Terabyte guide to recovery. However
> Arch Linux also supports Syslinux as a bootloader and I haven't seen this
> warning in relation to Syslinux. So I wondered if it would be more stable
> to use Syslinux (although at present I have no experience of using it). I'm
> also looking at whether a separate small boot partition would be useful.
> Looking at the Syslinux installation guide it also assumes it will be
> installed into the MBR, so I expect I'll have to reinstall BIBM afterwards
> and find a way to get it to switch Syslinux to a partition.
> So my questions are:
> * Is Syslinux a viable option? (or should I stick with GRUB2 and take the
> risk of corruption of BIBM)
I have never used syslinux that way either, so can't provide a direct answer. One thing to be sure of is that it's config file (usually syslinux.cfg) will get updated automatically when the kernel package(s) get updated during normal system updates. Essentially all distros do this automatically for Grub. Hopefully that's what Arch means by "supports Syslinux as a bootloader", but I'm not sure of that.
Also, the problem you're describing sounds more like what happens when Grub is installed in the MBR by mistake, and not caused by it being installed in a boot sector. Installing/updating GRUB in the MBR will completely overwrite BIBM, and you won't see BIBM at all on boot. If Grub is installed in a partition boot sector, any kernel update from the distro would not affect BIBM itself at all. The failure mode there would be that Grub/Linux would not boot from the BIBM menu after BIBM otherwise starts normally.
> * Should I install the boot files (whether Syslinux or GRUB2) in a separate
> boot partition rather than the root partition?
It may be somewhat safer that way in the case of Grub, but FWIW, I don't do it that way on my own systems. I just have /boot as part of the root partition for simplicity. Here's another thread that gets into this general topic for more reading on it (see the last 3 or 4 posts in the thread):viewtopic.php?f=3&t=1664&hilit=core.img
> * Pointers to how to recover from Syslinux overwriting BIBM in the MBR?
If Arch does support using Syslinux installed to a partition as the system bootloader, then that shouldn't happen. Any updates should not touch the MBR/EMBR, so that BIBM is not affected.