Load/Unload State Memory

Load/Unload State Memory

   This article describes an idea to log the history of the
drive state, especially for the load/unload system in HDD.

   The design of the system to prevent the head to land on
the disk is one of the most critical part in the Ramp Load/Unload
Technology.  In order to establish and brush-up this safety net
system, a new idea is proposed here which logs the drive state
history, and trace it later on failure analysis.  In general, "Head
land on the  disk" means head_to_disk stiction in Load/Unload HDD.
Thus the most useful information is the drive state just before the
Land on the Disk.  So
  1.  Will start to Load: Load Command has come
  2.  Unable to Load: Load Fail State
  3.  Load Completed: Head is on the rotational disk
  4.  Will start to Unload: Unload Command has come
  5.  Unable to Unload: Unload Fail State
  6.  Unload Complete: Head is on the Ramp should be stored
      for the information used later.  This invention
      proposes that those information to store on the non-volatile
      memory; such as EPROM.  By doing this, this information can
      be loaded from outside even if the head stuck on the disk.