It's the ICH8 Family, including 82801 PCI Bridge-244E, 82802 Firmware Hub, ICH8 Family SMBus Controller-283E, ICH8DH LPC Interface Controller-2812, P965/G965 PCI Express Root Port-29A1, and P965/G965 Processor to I/O Controller-29A0.
In the meantime, I followed a link provided by Hawkeye52 regarding a RAID 1 system, and realized I needed to select "Rebuild to this hard drive". That seemed to add the replacement HD listed as non-RAID disk to the volume and it is now rebuilding (a 12 hour process for a 500 GB volume). Please let me know if I need to do anything else! So now, assuming this results in restoring my RAID volume intact, the question is what to do to increase the size of the volume to take advantage of the larger HDs available (my replacement drive is 1TB). The link from Hawkeye52 included mention of this for a RAID 1 system but it's not apparent how to do this for a 3-drive RAID 5 system. I'm guessing I need to reset all the disks to non-RAID, replace the remaining 2 drives with 1TB drives, resize the primary HD for a 1TB partition, and then "create a RAID volume from existing HD". I don't know what would happen if the HD partition reset to non-RAID is too small to hold all the data from the original volume. Here's the link for reference: http://download.intel.com/support/chipsets/imsm/sb/imsm_reference1.pdf
Thanks for the reassurance, Victor. I have been very nervous playing with the guts of my system. Like magic, the rebuilding brought my new HD into the RAID volume and removed the "missing drive" message. Life is good.
BTW, if your Intel colleagues would amend the imsm_reference1.pdf to add a note to right-click on the (new) non-RAID drive and choose "Rebuild to this hard drive" in item #5, it could head off inquiries like mine.
Do you or anyone else have guidance on how to expand the RAID 5 volume size from its current 500GB to 2TB if I replace the other two HDDs with TB drives (to have 3x1TB HDDs)? Or would I be pushing my luck?