In almost every case I've ever seen of a drive B it's a partition windows creates to store its pristine CAD files or a partition created by an OEM to keep its factory original repair files. But B drive will be a partition on C drive. I've never seen an added drive get 'given' B as a drive spec, additional drives are lettered above C (plus optical reservation ), so usually start at E and go upwards. Drive A being reserved for floppy.
So the only way you'd get a 100Mb partition on that drive would be if it's a used drive that someone had as a boot drive for OS, replaced it and was smart enough to format both B and C, but not smart enough to bypass the boot partition lock.
Many people in returns departments would just check to see if...