This is a count of buffered I/O operations, i.e., I/O requests that pass through an intermediate system buffer, performed system-wide since the system was booted. An administrator monitors this counter to understand overall buffered I/O load on the system, which is typical of terminal and mailbox traffic rather than large data transfers. For example, a high vmsIoBufferedIO count relative to vmsIoDirectIO would suggest the system's I/O load is dominated by smaller, buffered transfers rather than bulk disk operations.