10-Memory - IV

10-Memory - IV - Memory - IV Presenter Tathagata...

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Memory - IV Presenter Tathagata Bhattacharjee
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Tathagata Bhattacharjee 2 Objectives In this chapter we shall discuss about the following: Magnetic Disk RAID Optical Memory Magnetic Tape
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Tathagata Bhattacharjee 3 Types of External Memory Magnetic Disk RAID Removable Optical CD-ROM CD-Recordable (CD-R) CD-R/W DVD Magnetic Tape
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Tathagata Bhattacharjee 4 Magnetic Disk Disk substrate coated with magnetizable material (iron oxide…rust) Substrate used to be aluminium Now glass Improved surface uniformity Increases reliability Reduction in surface defects Reduced read/write errors Lower flight heights Better stiffness Better shock/damage resistance
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Tathagata Bhattacharjee 5 Read and Write Mechanisms Recording and retrieval via conductive coil called a head May be single read/write head or separate ones During read/write, head is stationary, platter rotates Write Current through coil produces magnetic field Pulses sent to head Magnetic pattern recorded on surface below
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Tathagata Bhattacharjee 6 Read (traditional) Magnetic field moving relative to coil produces current Coil is the same for read and write Used in floppy disk systems and in older rigid disk systems Read (contemporary) Separate read head, close to write head Partially shielded magneto resistive (MR) sensor Electrical resistance depends on direction of magnetic field High frequency operation Higher storage density and speed
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Tathagata Bhattacharjee 7 Inductive Write/Magnetoresistive Read Head
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Tathagata Bhattacharjee 8 In contemporary rigid disk systems, there are separate read head, positioned for convenience close to the write head The read head consists of a partially shielded magnetoresistive (MR) sensor The MR material has an electrical resistance that depends on the direction of the magnetization of the medium moving under it By passing a current through the MR sensor, resistance changes are detected as voltage signals.
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Tathagata Bhattacharjee 9 The MR design allows higher-frequency operation, which equates to greater storage densities and operating speeds.
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Tathagata Bhattacharjee 10 Data Organization and Formatting Concentric rings or tracks Gaps between tracks Reduce gap to increase capacity Same number of bits per track (variable packing density) Constant angular velocity Tracks divided into sectors Minimum block size is one sector May have more than one sector per block
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Tathagata Bhattacharjee 11 Disk Data Layout
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Tathagata Bhattacharjee 12 Tracks Concentric rings Adjacent tracks are separated by gaps Gaps prevents or minimized errors due to mis-alignment of the head or simply interference of magnetic fields
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Tathagata Bhattacharjee 13 Sectors Data are transferred to and from the disk in sectors. Hundreds of sectors per track
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This note was uploaded on 07/15/2011 for the course ECO 2023 taught by Professor Mr.raza during the Summer '10 term at FAU.

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10-Memory - IV - Memory - IV Presenter Tathagata...

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