Directory Based Cache Coherency, Organization, Operations and Challenges in Implementation - Study

Today's 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 purpose of this number is to mention the locations of block copies. 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. This paper discus different Directory Based implementation, operations along with and its implementation difficulties