A Closer Look II (Read)
- Dirty bit ON -- controller sends reply to Px of processor with Id, Py of owner
- Px controller sends request to owner Py for data
- 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; notice yth presence bit remains ON
This is essentially the protocol for the LLNL
S-1 multicomputer from late ‘70s