Introduction to hard drive technology

SATA-IO

The term ‘SATA II’ is often used, incorrectly, to indicate that a drive has a 300MB/sec interface. The organisation that penned out the features of the newest SATA standard was named ‘SATA II’ which is where the confusion came from; the name is now changed to SATA-IO in an attempt to stop manufacturers from using incorrect terminology.

A 300MB/sec interface is only one of the many specifications included in the most recent SATA standard. The full list of features in the latest SATA specification includes the following:

3Gb/s interface bandwidth – This is the 300MB/sec bandwidth that everyone is familiar with.

ClickConnect – A locking drive connector, provided by a clip similar to what is on an Ethernet connector. The end of the SATA cable that connects to the drive has a small metal clip on it that prevents the cable from becoming dislodged accidentally.

eSATA and xSATA – External SATA specifications, with a longer cable lengths than internal SATA (2m and 8m respectively) and a different cable design.

Hot-plugging – The ability to plug or unplug a drive while the host system is active.

NCQ – as explained on the previous page.

Link Power Management – this provides additional power management functionality to a device.

Staggered spin-up – this feature is often used in large RAID arrays. A hard drive uses far more power when powering on than when sitting idle. Staggered spin-up reduces the load on a power supply by powering on one drive after another, instead of an entire array at the same time.

Asynchronous Notification – this is a feature which allows a device to notify a controller that it requires attention.

Chances are you’re not particularly bothered about most of those features. The interface bandwidth is the feature that easily stands out the most, which is perhaps the reason that the term SATA II is sometimes used to indicate this. The added bandwidth is the feature that most people are after when they’re buying a ‘SATA II’ drive. Twice the bandwidth of an older drive would indicate that there is quite a performance increase, but this isn’t the case.

A 300MB/sec interface doesn’t necessarily mean that the drive can actually sustain that amount of bandwidth; in fact, there is currently no SATA drive available that is capable of coming close to saturating the 150MB/sec maximum of the original SATA interface. Current drives sustained transfer rates don’t even exceed the bandwidth provided by the ATA/133 interface.

The only performance difference between a SATA/150 drive and a SATA/300 drive is the speed at which the drive’s cache can be read and written. While this does improve performance, the increase is marginal at best. The added bandwidth is there to provide headroom for future devices. There will be a 600MB/sec interface around well before the current 300MB/sec becomes a bottleneck.