Patent US 4,298,929

A data processing system including at least one channel and a multilevel store has the capability of performing a channel write to main memory where the data to be written into main memory crosses a double word boundary in a partial write store. The partial write store is accomplished by a merge operation which takes place in the memory system in a manner such that the main processor, channel and a cache store are freed up for further operation prior to the completion of the write to main memory.