This is a count of direct I/O operations, i.e., I/O requests handled without going through an intermediate system buffer, performed system-wide since the system was booted. An administrator monitors this system-wide counter to gauge overall direct I/O load, complementing the per-process sPsDirectIO figures. For example, a high vmsIoDirectIO count alongside one process showing an outsized sPsDirectIO value would confirm that process is responsible for most of the system's direct I/O load.