Abstract: Method and apparatus for use in a computer having peripheral data storage, to monitor data transfers to detect defective or marginally defective storage areas. The method and apparatus are based on a memory-resident program component and a transient program component which cooperate. The resident component is in the computer's interrupt chain, to be invoked during both the initiation and conclusion of storage operations. When a data access is called, a timer (e.g., the system timer) provides interrupts at a suitably high rate, and informs a second component of the operation. At the conclusion of the operation, error indications are logged into a log file. The second component accumulates interrupts during the operation, and monitors one or more memory addresses. For each monitored address, when its contents first change, the second component stores the current interrupt accumulation.