[CentOS] a hardware question

We need to replace several servers, quickly - four of our Dell PE 1950's
died in one week. (!!!) So, we're looking around, and I was checking out
IBM. I customized to what we want, and hit 'continue', and suddenly
there's another $800 for a "system common planar" that's "required".
Googling only finds specs with it - does anyone know what it is? I mean,
it's not like it's the motherboard, right?

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