Abstract: In a data processing system, there is included a central processing unit (CPU) and a main memory for storing computer words, the CPU including a cache unit. In operation, the CPU requests that a computer word be fetched, the computer word to be fetched being identified by a real address location corresponding to a location where the predetermined computer word is stored in main memory. The CPU request to fetch the computer word is coupled through the cache unit such that the cache unit determines whether the computer word is stored within the cache unit. The cache unit comprises a cache for storing predetermined ones of the compter words. A directory is included for storing partial real address information to a corresponding computer word stored in the cache. A detecting element, operatively connected to the cache and to the directory, determines when a hit occurs without any errors.