IPMI: What is “Planar” temperature?

Question

I'm digging through the output of ipmitool sdr list on a Dell PE R710 - and I see there's a sensor reading named "Planar Temp" - which reads higher than the ambient temperature but lower than the CPU temps.

Both entities for "Ambient" and "Planar" are a part of the board; What is "Planar Temp" referring to in this context?

Answer 1

It's the temperature of what you probably think of as the "motherboard".

Not everyone calls them motherboards. They've been called mainboards, system boards, planar boards, logic boards, and baseboards. Winn L. Rosch gives the gory details, including the subtle differences.

Further reading

• Winn L. Rosch (2003). "Principles: Hardware" § Nomenclature. Winn L. Rosch hardware bible. 6th Edition. Que Publishing. ISBN 9780789728593. pp. 973–974

Answer 2

The planar relates to the PCI bus. It's the integrated circuits on the motherboard, as opposed to a riser card.