Booting a linux system is handled by what is known as a bootloader. Arch-Linux offers a variety of such bootloaders and the process is “nearly” identical to Arch-Linux with one exception. S6 prefers the root partition to be mounted initially as ro (read only) and only after its own checks S6 remounts it rw (read write). For example in a syslinux boot entry it may look like this in arch:
LABEL Obarun-Linux LINUX /boot/vmlinuz-linux INITRD /boot/initramfs-linux.img APPEND root=/dev/sda5 rw quiet net.ifnames=0
In Obarun you must manually edit /boot/syslinux/syslinux.cfg to:
LABEL Obarun-Linux LINUX /boot/vmlinuz-linux INITRD /boot/initramfs-linux.img APPEND root=/dev/sda5 ro quiet net.ifnames=0
Grub2 and Syslinux which are the most commonly used software are offered through the installer and you can choose the one or the other. For other bootloaders you should consult the Arch-Wiki. Note that grub-legacy is still available through the AUR repository as AUR/grub-legacy.
For multiboot (booting different systems with one bootloader) you may use os-prober as an add-on to grub but we do not recommend it as it is very unreliable. It is best to seek information on the boot entries preferred by each particular system and make a file in /boot/grub/custom.cfg to add them. For ms-windows installations generally os-prober is sufficiently reliable.