I was under the impression, (perhaps incorrect), that mismatched capacity pairs, installed in a dual channel board, *(obviously one DIMM in each channel) would still run in dual channel mode, up to the capacity of the smaller stick, and only the differential memory would revert to single channel. Intel calls this "flex mode", and explains it thus:
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.
Related to
In the provided link, I believe THW member "sadams04", explains this aspect of Intel dual channel memory configuration incorrectly: The ?61 chipset in that board is well new enough to have the "flex memory" available, should it be needed.
"You have DDR3-1600 modules which are scaling down to DDR3-1333 (the max your board supports). (good so far),
Having non-matching sized 2GB and 4GB modules will have you running in single channel mode (reduced performance) while your motherboard is capable of dual channel mode. Always install modules in matching pairs to take advantage of the dual memory controllers. Your options are to remove the 2GB module, then install a matching 4GB DDR3-1600 CL9 module (2 x 4GB for 8GB in dual channel mode), or remove both modules and install a matching pair of 8GB modules (2 x 8GB DDR3-1333 or DDR3-1600)".
Here's the link to Intel's full page of memory configuration data, with dual, triple, & quadruple channel systems explained:
https://www.intel.com/content/www/us/en/support/articles/000005657/boards-and-kits.html
