During nonsynchronous operation mismatch detection not available so there may be a long period of time during which mutilation occurs. Mismatch detection useless in finding data mutilation caused by program bugs. Audit programs detect bad data.
Audits run periodically or as requested from tty.
Separate audits for different memory blocks Audits correct by idling memory blocks containing bad data. System recovery initiated by control unit switch during simplex operation, control unit switch can be caused by bad data or bugs that cause sanity time out. Make call store consistent with state of periphery. Reinitialize memory structure - fast, disturbs many calls. Use sanity timers Call audits or reinitialize system to correct errors.