Command Queuing

7/31/2019 Command Queuing

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Submitted by : Soumyajit ChandEC-06-56

0601230304


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Command Queuing Dissecting an HDD Types of HDD Connection

PATA & SATA Comparison between PATA &SATA Technology used in HDDs TCQ NCQ Conclusion References


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Command Queuing is a technology that allows to sendmultiple read and write requests to a hard drivesimultaneously.

CQ can improve the overall performance of a hard drive if itis implemented correctly.


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PATA(Parallel Advanced Technologyattachment)

SATA(Sarallel Advanced Technologyattachment)


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Parallel flow of data Cables are 40 pin wide

Energy consumption 5 volt TCQ technology used


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Serial flow of data Cables are 7 pined

Energy consumption less of 250 mv NCQ technology used


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Seek Latency

Rotational Latency


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Tagged Command Queuing

Native Command Queuing


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TCQ stands for the Tagged Command Queuing technologybuilt into certain PATA HDDs.

Before TCQ ,how the commands will be sent to the HDD and

in what order they will be executed was decided by the OS. Moreover, the OS was able to send only one command at a

time which was a major limitation for faster operation of theHDDs.

The traditional method was inefficient as it consumes moretime.

HDDs that employ TCQ have control over the executionorder of the commands.


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TCQ provides HDDs total control and freedom over thecommands sent by the OS.


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DMA not supported

Data transfer slow

Interference of cpu


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Native Command Queuing achieves high performance andefficiency through efficient command re-ordering. Inaddition, there are three new capabilities that are built into

the Serial ATA protocol to enhance NCQ performanceincluding race-free status return, interrupt aggregation, andFirst Party DMA


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Race-Free Status Return Mechanism

Interrupt Aggregation

First Party DMA


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Building a queue of commands in the drive

Transferring data for each command

Returning status for the commands that werecompleted


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Mans desire for faster data transmission rate is gettingsatisfied as technology improves. While it was only possibleto read/write data from/to an HDD in some MBps only few

years back, now the rate is in GBps. With the advent of betterqueuing techniques like NCQ, and interfacing methods likeSATA, HDDs now operate faster giving the performance ofthe system a boost.


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http://www.google.com

http://en.wikipedia.org http://www.wdc.com/en/library/sata/2579-001076.pdf
http://www.google.com/http://en.wikipedia.org/http://www.wdc.com/en/library/sata/2579-001076.pdfhttp://www.wdc.com/en/library/sata/2579-001076.pdfhttp://www.wdc.com/en/library/sata/2579-001076.pdfhttp://www.wdc.com/en/library/sata/2579-001076.pdfhttp://en.wikipedia.org/http://www.google.com/


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Command Queuing

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