[ros-users] How much RAM is needed for a minimal ROS

I am new to ROS. My interest is using a minimal ROS
running on Ben Nanonote[1] a very small Linux (OpenWRT)
computer as a way to communicate with target sensor platforms.

Can someone say roughly what the minimum RAM requirment
is for ROS?

[1] http://qi-hardware.com
Thanks

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Ron K. Jeffries