Facet API: grouping indexed values into several drop-down facets
If possible, I'd use a vocabulary for each of the facets ('dropdowns'). Add a term referenece field to your node for each of those as well. Then add these fields to your search index and add the facets for them.

E.g.,
Vocabulary:
CPU

Terms: 
Core i5
Core i7
...

Vocabulary:
Memory

Terms:
4 GB
8 GB
..