To be simple, you only have to have tow partion. And if your memory is big enough. You can have a single partion as "/".
In the old days, the bios don't support a system to boot from a partion beyond 1024 cylinder. And people have to make "/boot" a separate partion, to make the system bootable.
Nowadays, almost all bios support booting from after 1024 cylinder. If your computer is younger than 4, it is likely a modern one.