HARD DISK DRIVE (HDD) IN ORDER TO PROVIDE DATA-STORAGE MEDIUM FOR DATA-PROCESSING SYSTEMS SUCH AS COMPUTERS WAS INTRODUCED IN 1986. THEN, ITS PERFORMANCE HAS IMPROVED DRAMATICALLY AND VARIOUS KINDS OF TIME OPTIMAL CONTROL (TOC) SUCH AS PROXIMATE TIME OPTIMAL SERVOMECHANISM (PTOS) HAVE BEEN IMPLEMENTED ON HDD SERVO SYSTEMS. IN THIS PAPER, AN OVERVIEW ON SOME IMPORTANT KEY TOPICS OF THE RESEARCHES ON HDD SERVO SYSTEMS INCLUDING HDDS, SINGLE STAGE HDD SERVO SYSTEMS AND DUAL STAGE ACTUATOR (DSA) SYSTEMS ARE DISCUSSED IN DETAILS. ALSO, A CONSIDERABLE PART OF THIS WORK PROVIDES THE DIFFERENT NEAR TOC ALGORITHMS.