how meany are computers install OS on it in the same time ?

RouterOS Beginner Basics
1

i will buy a licenses

how meany are computers install OS on it in the same time ?

mybe the machine brocken down and transfer Os on other computer

wt i do ?

2

No license are install only on 1 HDD and cannot transfer to other

3

And if your HD failed, you will lose your license, so try to use the best hardware you can get.

http://wiki.mikrotik.com/wiki/All_about_licenses