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Test: 6 HDD SATA 3 Gbits /s 250 GB
by Marc Prieur
Published on May 31, 2006

Since our last test, manufactures had time to launch one (and sometimes two) generations of hard drives. We thought that it was time to take stock on one of the slowest element of computers, the hard drive. For this survey, we chose 6 Serial ATA 3 Gbits /s 250 GB /s, which run at 7200 rpm.
Some will be surprised by the title of this article since it doesn’t mention SATA II but rather SATA 3 Gbits /s. This is perfectly normal because the SATA II norm doesn’t really exist.

Indeed, after finalizing the specifications of the Serial ATA 1.0 norm at the end of 2001, several industries formed the Serial ATA II Working Group, which has since been renamed the Serial ATA International Organization or SATA-IO. Their aim was to create a « superset » for the Serial ATA 1.0 or extend its specifications.

Several additions were made, which are independent. The two most important are Native Command Queuing (NCQ) and 3.0 Gbits /s. A Serial ATA drive can have the NCQ defined by the SATA II work group without benefiting from a 3.0 Gbits /s, whereas another can have this interface but not support the NCQ.
Before continuing this article we would like to cover the basics of these two specifications. In principle, Native Command Queuing is relatively simple. It allows the drive to execute write /read commands that are transmitted randomly in order to optimise the movement of the reading head.

Speed is increased but there is also an impact on power consumption and noise level which is reduced. Of course, applications don’t have to work simultaneously and don’t have to wait for the previous result to send the next command. This of course isn’t always possible. Another possibility in using NCQ is multitasking in the case where you run two very heavy applications simultaneously from the drive point of view.

To better explain this situation, imagine an elevator, in which two people enter simultaneously on the ground floor. The first pushes the 12th floor button and the second the 2nd floor. It would be counterproductive to go to the 12th floor and then to the 2nd floor. The principle of NCQ was already in the ATA norm since 1997 with TCQ (Tagged Command Queuing). This heavier protocol could sometimes lead to significant performance losses in the case of low loads (no or very little command reorganisation to do) and has been integrated in a limited number of controllers. Hitachi supports it on 7K250 drives, like Western and the Raptor WD740GD, while on the chipset side, we can count on NVIDIA but not Intel.

SATA 3.0 Gbits /s defines a new speed of data transmission for the Serial ATA interface. Initially, SATA reached up to 1.5 Gbits /s, which really corresponds to 150 mega-octets per second as 20% of information is dedicated to error correction. The transfer rate is now increased to 300 MB/s but we have to keep in mind that this is the interface speed. It has nothing to do with disc speed alone. At most, cache speed would be affected.

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