Fundamental of HDD Technology (1)

Transcription

1 Course Information Fundamental of HDD Technology (1) Data Storage Technology Research Unit Nakhon Pathom Rajabhat University Assistant Prof. Piya Kovintavewat, Ph.D. URL: Instructors: Assist. Prof. Piya Kovintavewat, Ph.D. Class: Saturday s: Office Hour: After class Books: Magnetic information storage technology, S. X. Wang and A. M. Taratorin Magnetic Recording Systems and Measurements, A. M. Taratorin Digital Baseband Transmission and Recording, J.W.M Bergmans ป ยะ โคว นท ทว ว ฒน, การประมวลผลส ญญาณส าหร บการจ ดเก บข อม ลด จ ท ล เล ม 1: พ นฐานช องส ญญาณอ าน-เข ยน, ศ นย เทคโนโลย อ เล กทรอน กส และคอมพ วเตอร แหงชาต (เนคเทค), ป ยะ โคว นท ทว ว ฒน, การประมวลผลส ญญาณส าหร บการจ ดเก บข อม ลด จ ท ล เล ม 2: การออกแบบวงจรภาคร บ, ศ นย เทคโนโลย อ เล กทรอน กส และคอมพ วเตอร แหงชาต (เนคเทค), ป ยะ โคว นท ทว ว ฒน, ค ม อโปรแกรมภาษา SCILAB ส าหร บผ เร มต น (ฉบ บปร บปร ง), โรงพ มพ เพชรเกษมการพ มพ, Course Syllabus Types of Memory, Magnetic Anisotropy, Magnetic Materials (LMR, PMR, HAMR), Magnetic Recording Process, Magnetic Replay Process, Transitions Effects, Understanding Heads, Thin film & Particulate Media, Transition parameter/pw50/d50/roll off curve, Track edge &Track width effect Read/Write Technology, Losses in Magnetic recording, HDD Mechanics, Electronics, Servo Writing Technology, Drive System Parameters, Understanding Channel & Coding, HDD Controller Course Syllabus Grading: Attendant & HW (20) Project (10) Midterm (30) Final (40) Q&A Session: Should one has any question or help on the homework, ask me after class or me. Absence of Exams: Please tell me in advance if you will be absent, only legitimate reasons are noticed. In case of sickness, bring proof together with the doctor s phone number

2 Outline Memory/Storage Hierarchy Introduction to HDD What is magnetic recording? Magnetic recording HDD structure HDD model Hysteresis loop Superparamagnetic Effect Magnetic Anisotropy HDD technology trend (Microprocessor, DRAM) (CD-ROM, DVD, Magnetic tape/disk) SOURCE: First Disk Drive First Disk Drive IBM 305 RAMAC Magnetic recording was first described in 1888 [Smith 1888] and first demonstrated in 1898 [Poulsen 1898] in the form of Telegraphone*. The first production disk drive was introduced in 1956 by IBM and was called the IBM 305 RAMAC (random access method of accounting and control). The IBM 305 RAMAC could store five million characters (five megabytes = 5 MBytes) of data on 50 disks, each 24 inches in diameter. * Analog voice signals were stored on a steel piano wire that was wound spirally around a rotating drum. SOURCE:

3 HDD Roadmap Areal Density Trend Notation: Areal density = a traditional measurement for disk drives to determine capacity, internal (media) data rate, and finally price per unit of capacity. CGR = compound growth rate SOURCE: SOURCE: Internal Data Rate Trend Average Price of Storage (Dollars/Bytes) SOURCE: SOURCE:

4 Hard Disk Drive (HDD) Overall HDD Structure SOURCE: BNikolic/BWRCLunch-Storage.ppt Internal HDD Structure Magnetic Recording Model x k a k âk xˆk

5 Data Structure 2 ( bits/in. ) ( bits/in. ) ( tracks/in. ) HDD stores information on circular magnetic disks called platters. Each platter has magnetic material coated on both the surfaces. On each surface, data is stored along concentric circles called tracks. Each track is subdivided into sectors, each of which holds 512 bytes of data. One sector consists of Preamble Address mark Data Track Sector Hysteresis Loop M s M M r -Hc M = Medium magnetization H = Applied magnetic field H -M s H c -M r Media with large Hc Difficult to write data (require high H) No disturbance from adjacent tracks

6 Superparamagnetic Effect Fact: Currently, the storage capacity and the speed of HDDs keep increasing, while their price keeps decreasing. As HDDs become capable of storing more information and accessing it at faster speeds, their data becomes more susceptible to corruption. This data-density barrier is known as the superparamagnetic effect. Superpamagnetic effect: Destabilize the 0 and 1 -orientation of magnetic bits, resulting in corruption of stored data (i.e., when the energy in the bits atoms approaches the thermal energy around them, the bits start randomly switching between 0 s and 1 s). The actual data bits consist of sub-micron sized grains Over long period of time, some of these grains will switch (by heat) and cause data loss Small grains usually switch first!! Super paramagnetic limit: The limitation on the magnetic grain size, if the grains are smaller than this size, the data is lost instantaneously right after recorded This prevents us from achieving higher density by shrinking bit size and grain size For a single domain particle (like a grain in media), the probability of magnetization reversal per unit time can be approximated by the Arrhenius equation: f = f 0 e KV k T KV constant M kt = > B B where f 0 = attempt frequency = 1 GHz K = Anisotropy constant Hc/2Ms V = particle volume k B = Boltzman constant T = temperature Basically, data written in the media will be stable if and only if where M is a constant with a large value, i.e., M = 60 To increase the storage capacity, we need to Reduce V Increase K Keep Because K Hc/2Ms Hc Ms Higher Hc (limited by writer ability) Lower Ms (limited by reader ability) KV constant kt = Perpendicular Use small V to store a bit require high H B

7 How to Increase Storage Capacity Some possible solutions to increase storage capacity: Reduce the head flying height Reduce the gap size in the head Reduce the media thickness Employ advanced signal processing methods Use advanced digital integrated circuits Move recording systems to perpendicular recording Signal processing is increasingly recognized as a costefficient means of improving storage capacity [Moon 1998]. A r e a l D e n s i t y [ Gbits/in2 ] Longitudinal / Perpendicular Recording Heat-Assisted Magnetic Recording (HAMR) M M r M r H c H c H

8 Alternative Data Storage Technologies Holographic Storage Potential: Very low cost media $10/TB? (possibly removable and re-writable) High capacity (in TB) High data rate (100 s MB/s) Ultra fast search potential (1 Gb/ns?) SOURCE: BNikolic/BWRCLunch-Storage.ppt Patterned Media Lithographically Patterned Magnetic Elements Source: MIT Nanotechnology Lab