Rotational hard disks have a controversial (mis)feature which automatically unloads the read/write heads during perceived inactivity, usually within 10 seconds. Western Digital calls it "Intellipark", but the problem is present in other manufacturers' disks as well, and goes back to at least the mid-2000s.

Frequent parking leads to noticable latency on wakeup, and the hard retraction is seen as an impediment to disk life. Even with various utility programs, this parking feature is not reliably deactivatable. (See "Comparison" section below.)

The "parkverbot" daemon will issue small read requests periodically to a random location on disk in an effort to reset the inactivity timer in the hardware and so prevent the dreaded head unloading. As such, its operation is non-destructive and interoperable across different brands of hard drives and transports.

The current block reading algorithm works reasonably well in practice: the worst observed head parking rate was about 3 unloads/day (0.125/hour); best figures hover around 0.5 unloads/day (0.021/hour).