LOCALIZATION APPROACH IN DIRECTORY BASED CACHE COHERENCY AND ITS IMPACT ON CACHE COHERENCY IMPLEMENTATION- STUDY.

Todays systems are designed with Multi Core Architecture. The idea behind this is to achieve high system throuput. Once the Processor clock speed reached its saturation, designers opted for having multiple cores. Each Core or Processor equipped with their own private cache memory. But under Chip Multiprocessor, where all the processor have access to shared memory, having respective cache memory will result with Cache Coherency Problem. In Directory Protocol, for each block of data there is a directory entry that contains a number of pointers. The important advantage of directory based protocols is that they scale much better than snoopy protocols. In addition to this it has the advantage of ability to exploit arbitrary point-to-point interconnects. But mean time it also has the overhead in terms of the storage and manipulation of directory state. Communication cost is one of the major issue which accounts for the performance of Directory based cache coherency systems. Having the directory maintained with local memory always gives better performance. This paper discus different Directory Based implementation, in terms of its locality and its implications on the systems.