On Sat, Mar 12, 2016 at 12:32 PM, Noel Chiappa <jnc at mercury.lcs.mit.eduwrote: The ISOLTS (Isolated Testing Subsystem) performs CPU diagnostics on multi-CPU systems. It dynamically reconfigures Multics to take the one of the CPUs offline and to reserve a bank of memory in one the SCUs (the memory is still visible to Multics, but reserved for ISOLTs use). The offline CPU is hung at a 'Delay until interrupt' instruction. The memory configuration switches are then set on the offline CPU so that the reserved block of memory appears to that CPU as a 128K block of memory starting at location 0. ISOSLTS when installs a bootstrap loader in the reserved memory block, with an entry at the interrupt handler vector. ISOLTS sends an interrupt to the offline CPU, the interrupt vector transfers to the bootstrap loader, which sets a flag in memory indicating that all of that reconfiguration was done correctly. ISOLTS sees the flag set, and then starts loading tests into memory and running them by setting the interrupt vector and interrupting the CPU, and watching memory to see the test results. When the tests are done, the CPU configuration switches are set back, the SCU memory is released, and Multics brings the CPU back online. I get bloody impressed just watching it on the emulator; doing it in a production environment must have been spectacular. -- Charles Noel