With many Intel processors flex mode is possible:
Flex mode
This mode results in both dual and single-channel operation across the whole of DRAM memory. The figure shows a flex mode configuration using two DIMMs. The operation is as follows:
• The 2 GB DIMM in slot 1 and the lower 2 GB of the DIMM in slot 2 operate together in dual-channel mode.
• The remaining (upper) 2 GB of the DIMM in slot 2 operates in single-channel mode.
flex