Innards

What's the main difference between these two processors.. Dual six core Xeon e5645 & just six core Xeon e5645? And what does a chipset do? Have put some memory in one & changed power supply & video cards, but that's about it, don't really know the inner workings so any clarification would be appreciated, thanks.. Also have a choice of PERC6/i SAS/SATA Hardware RAID Card - For Connecting Internal Hard Drives or SAS 6i/R Controller Card - For Connecting Internal SAS Hard Drives. Or will the default thing Integrated Intel chipset SATA 3.0Gb/s controller be ok?

( Have this thread in another part of forum too.. Didn't know which place would be best ..)