A hierarchical cache structure comprises at least one higher level cache comprising a unified cache array for data and instructions and at least two lower level caches, each split in an instruction cache and a data cache. An instruction cache and a data cache of a split second level cache are connected to a third level cache; and an instruction cache of a split first level cache is connected to the instruction cache of the split second level cache, and a data cache of the split first level cache is connected to the instruction cache and the data cache of the split second level cache.