Native Command Queuing (NCQ)

NCQ is used to improve the hard disc performance by re-ordering the commands send by the computer to the hard disc drive. Native Command Queuing (NCQ) is an extension of the Serial ATA.

HARD DISC DRIVE

limitation of Parallel ATA limitation of Parallel ATA is the difficulty in increasing the data rate beyond 100 MBytes/s. Parallel ATA uses a single-ended signaling system that is prone to induced noise Parallel Advanced Technology Attachment

SATA (Serial Advanced Technology Attachment) Serial ATA (SATA) is a computer bus technology. Designed for transfer of data to and from a hard disk. Serial ATA is a serial link — a single cable with a minimum of four wires. It creates a point-to-point connection between devices

Serial ATA (SATA) is an interface used to connect hard drives and other peripherals to a PC. It creates a point-to-point connection between devices This interface will be used to connect storage devices such as hard disc drives, DVDs, and CD- R/Ws to the motherboard

NEED FOR SATA The 5-volt signaling requirement and high pin count (40-pin cable connectors) The 18-inch cable length limitation; cable width and cable routing problems Data robustness issues

Serial ATA Topology Application 1 Application 2 Application 3 Serial ' ATA Adapter

BENEFITS OF SATA Serial ATA is faster Reduction in voltage Cabling Improved Data Robustness Backward Compatibility Increased Disc Drive Data Rates Serial ATA Integration Connectivity

LAYERING MODEL The Transport and Link layers control overall operation. Application layer is designed to maintaining software compatibility The Physical layer handles the high speed serial communications between the host and device. Serial ATA Communications Layer Model 4Application 3Transport 2Link 1physical

General Advantages of Queuing Hard Disk Drive (HDD) is the slowest component in the system data transfer chain An improvement in efficiency of moving data to and from the disk can be achieved if circumferential and radial mechanical motions are optimized by reordering the sequence in which these locations are reache d

DESCRIPTION OF NCQ

SEEK LATENCY &ROTATIONAL LATENCY SEEK LATENCY It are caused by the time it takes the read/write head to position and settle over the correct track containing the target LBA. ROTATIONAL LATENCY It is the amount of time it take for starting LBA to rotate under the heard after the head is the right track.

BENEFITS OF NCQ Race-fire status Return mechanism Interrupt aggregation First party DMA

DETAILED DESCRIPTION OF NCQ 3 Main components of NCQ Building a queue of commands in the drive Transferring data for each command Returning status for the commands that were completed

Components of NCQ Command queue building in the drive: A SATA NCQ drive can either queue commands or execute them immediately. The drive knows what protocol to apply to different commands. It assigns a unique tag to commands. Transferring data for each command: NCQ lets the drive set up a direct memory access (DMA) operation for a data transfer without host software intervention. The drive controls the DMA engine, selects transfers to minimize latencies, and optimizes command ordering. Returning status for completed commands: The drive returns a status for completed commands. Command status is race-free, which means a status for any command can be communicated at any time, without a handshake between device and host

ADVANTAGES OF NCQ NCQ is designed to improve performance and reliability as the transactional workload increases When your application sends multiple commands to your drive, your drive can optimize the completion of these commands to reduce mechanical workload and improve performance Devices that support NCQ are 100% backward compatible with non-NCQ supporting systems

Command queue building in the drive: A SATA NCQ drive can either queue commands or execute them immediately. Transferring data for each command Returning status for completed commands

CONCLUSION NCQ has the potential to offer significant performance advantages. The benefits of NCQ are realized when a queue of commands is built up in the drive such that drive can optimally re-order the command to reduce both seek and rotational latency. NCQ delivers an efficient solution through features in the several ATA protocol including race free status return, interrupt aggregation and first party DMA.

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