A method, a computer program, and an apparatus are provided for flexible SC to SR mapping to enable sub-page activation in an XDR.TM. memory system. An XDR.TM. memory system may allow system page size to reduced by a factor of two (half-page activation) or four (quarter-page activation). In an XDR.TM. memory system there are five different SCs and two different SRs. This scheme allows any one of the five SCs (or none) to be mapped to any one of the two SRs. Overall, this invention provides a flexible mapping scheme that can be utilized for any possible XDR memory system.