Ch. 4 - Hard Disk and Buses

Ch. 4 - Hard Disk and Buses - 2/23/2010 CET 3503...

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2/23/2010 1 CET 3503 MICROCOMPUTER TECHNOLOGY I ARCHITECTURE OF MICROCOMPUTERS – Addendum1 1 HARD DISKS: Heads: Induction coils (magnetizes the Track Heads: Induction coils (magnetizes the surface of the plates). Track: Concentric circles about the spindle, that hold the circular sequence of bits written as the disk makes a complete rotation. CET 3503 MICROCOMPUTER TECHNOLOGY I ARCHITECTURE OF MICROCOMPUTERS – Addendum1 2 HARD DISKS: Sector Track Sectors: each track is divided into a number of fixed-length sectors. (typically 512 bytes). Arms: move the heads in and out to different radial distance.
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2/23/2010 2 CET 3503 MICROCOMPUTER TECHNOLOGY I ARCHITECTURE OF MICROCOMPUTERS – Addendum1 3 HARD DISKS: Track width: Between 5,000 and 10,000 tracks per centimeter. Hard disk Performance: Seek time: Time used by the arm to move between random tracks. Between 5 to 10 ms (milliseconds). Rotational latency: Rotational latency: Once the head is positioned radially, the time elapsed until the desired sector of the track rotates under the head. CET 3503 MICROCOMPUTER TECHNOLOGY I ARCHITECTURE OF MICROCOMPUTERS – Addendum1 4 HARD DISKS: Typical disk rotates at 5,400 RPM, 7,200 RPM or 10,800 RPM. The average rotational latency for those values are: 5 5 ms 4 16 ms and 2 7 ms those values are: 5.5 ms, 4.16 ms and 2.7 ms. Transfer Rates: rate of moving bytes between the head of the disk to the controller. Typical values: 20 MB/sec to 40 MB/sec. A 512 byte sector takes between 13 μsec and 26 A 512-byte sector takes between 13 μsec and 26 μsec to get transferred to the controller. Why? So, the rotational time and seek time dominate the total transfer time.
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2/23/2010 3 CET 3503 MICROCOMPUTER TECHNOLOGY I ARCHITECTURE OF MICROCOMPUTERS – Addendum1 5 HARD DISKS: Disk Read Time Example: What is the average time to read or write a 512- byte sector for a typical disk rotating at 10,000 RPM? The advertised average seek time is 6 ms, the transfer rate is 50 MB/sec and the controller overhead is 0.2 ms. Assume that the disk is idle so there is no waiting time. CET 3503 MICROCOMPUTER TECHNOLOGY I ARCHITECTURE OF MICROCOMPUTERS – Addendum1 6 HARD DISKS: Disk Read Time Example: overhead Controller time transfer delay Rotational Average seek time Average time access disk Average + + + = sec/min 60 RPM 10,000 rotation 0.5 ms 6.0 time access disk Average + × + = ms 9.2 0.2 0.01 3.0 6.0 ms 0.2 MB/sec 50 Bytes 512 = + + + = + +
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2/23/2010 4 CET 3503 MICROCOMPUTER TECHNOLOGY I ARCHITECTURE OF MICROCOMPUTERS – Addendum1 7 CD and DVD’s: Optical media.
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Ch. 4 - Hard Disk and Buses - 2/23/2010 CET 3503...

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