http://www.mikrotik.com/testdocs/ros/2. ... rboard.php
cpu-mode (power-save | regular; default: power-save) - whether to enter CPU suspend mode in HTL instruction. Most OSs use HLT instruction during CPU idle cycle. When CPU is in suspend mode, it consumes less power, but in low-temperatire conditions it is recommended to choose regular mode, so that overall system temperature would be greater
What is this setting about: /system routerboard settings set cpu-mode=power-save|regular ?
Leave it on the default of power-save unless you will be experiencing temperatures below -15 Celcius (1 F), setting it to regular will help the CPU keep itself warm enough.
This setting should only be available on rb100 & rb500 series routers. Atleast I don't see it on my rb600 nor any rb4xx boards.