disk drive components

disk drive components - J. M. Harker D. W. Brede R. E....

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J. M. Harker D. W. Brede R. E. Pattison G. R. Santana L. G. Taft A Quarter Century of Disk File Innovation This paper traces the development disk file technology from the first disk drive to the present. A number innovative advances are reviewed in the evolution mechanical design, materials, and processes. These advances constitute the technological base that has permitted almost four orders of magnitude improvement in areal density; they are discussed interrelated aspects: the magnetic head and its air bearing support; the head positioning actuator; the disk substrate and its magnetic coating; and the readlwrite signal detection and clocking electronics. Introduction The first issue of the IBM Journal Research and Development in 1957 featured two papers, one describing the IBM 305 RAMAC system [ 11 and other describing 350 disk file [2]. As Stevens mentions in his overview paper“The Evolution of MagneticStorage” [3], the 350 was the first production movable-head disk drive. The purpose of this paper is to describe significant innovations that led to the introduction of that product the evolution of the current generation of disk file products. Inductive magnetic recording was selected as base technology for disk files because of its advantages of nonvolatility, immediate readback without intermediate processing, unlimited reversibility, and the relative low cost simplicity of the transducer recording medium. Increasing linear bit density has depended upon scaling down of the three geometric parameters of head- to-disk spacing, readwrite gap length, and disk magnetic coating thickness. Progress in reducing these key geomet- ric parameters resulting linear bit density of selected products is shown in Table 1. Achieving these reduced has been an iterative process required significant innovation. For example, scaling down coating thickness from 1200 microinches to 25 microinches has required extensive process develop- ment in the area of substrate preparation and magnetic film coating, formulation, application, buffing, and polish- ing. Reducing the spacing between the head and the disk from over 800 microinches to less than 13 microinches has required an in-depth understanding of air bearing technology through analysis, simulation and testing, de- velopment of low-mass sliders with very stiff air bearings, development of very smooth and flat disk surfaces with few mechanical asperities. Earlyrecording headcores were made of laminated mu-metal with the gap formed by a copper shim. Later, silicon dioxide was deposited on ferrite to form smaller, more precise gaps, most recently use of thin permalloy films and photolithographic techniques permitted extremely small and accurate dimensions for head gap, pole tip width, and pole tip thickness.
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disk drive components - J. M. Harker D. W. Brede R. E....

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