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http://w w w .stanford.edu/~ouster/cgi-bin/cs140-w inter12/lecture.php?topic=devices January 11, 2012 Storage Devices Storage Devices Lecture Notes for CS 140 Winter 2012 John Ousterhout Readings for this topic from Operating System Concepts : Sections 12.1-12.2. Magnetic Disk (Hard Drive) Basic geometry: 1-5 platters , magnetically coated on each surface Platters spin at 5000-15000 RPM Actuator arm positions heads , which can read and write data on the magnetic surfaces. Overall size of disk package: 1-8 inches. Organization of disk data: Circular tracks corresponding to a particular position of the actuator arm. Typical density today: 200,000 tracks per radial inch. Tracks divided into 512-byte sectors . Typical tracks contain a few thousand sectors. Typical total drive capacities: 100GB-2TB 100GB ~ 50M double-spaced pages of text. Disk technology is one of the most rapidly advancing technologies: capacities increasing faster than Moore's Law. Reading and writing: Seek : move actuator arm to position heads over desired track. Typical seek time: 2- 10ms. Select a particular head. Rotational latency : wait for desired sector to pass under the head. One-half disk rotation on average (4ms @ 7500RPM) Transfer: read or write data as it passes under the head. Typical transfer rates: 100-150 MBytes/sec. Latency
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This note was uploaded on 04/02/2012 for the course CS 140 taught by Professor Rosenblum during the Winter '08 term at Stanford.

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v12stanford.edu-Storage_Devices - Storage Devices http/w w...

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