A Closer Look (Read) II
•Dirty bit ON -- controller sends reply to Px of the processor ID of Py, the owner
•Px requests data from owner Py
•Owner Py controller, sets state to “shared,” forwards data to Px and sends data to home •At home, data is updated, dirty bit is turned OFF and the xth presence bit is set ON and yth presence bit remains ON
This is basically the protocol for the LLNL S-1 multicomputer from the late ‘70s