LOSTCIRCUITS		SHORTCUTS: Accepting a Narrow Bus Internal vs. Interface Performance HDTach: ATA vs. SATA HDTach vs. WinBench99 vs. PCMark Parallel ATA Command Overhead Streamlined SATA FIS, Prelude to Performance WinBench99 Overview Winbench99 Details Business Winstone2002, File Copy Conclusions Cheetahs and Cudas on the web Comments?
Seagate Barracuda SATA-V     Kudos to Cudas
(Review by MS, February 4)

We first forayed into Serial ATA technology as the storage media of the next decade almost 5 months ago. By now, the first Serial ATA drives, that is, different flavors of the Seagate Barracuda-V are already commercially available. Still, there is quite a bit of confusion surrounding Serial ATA technology particularly with respect to performance benefits over Parallel ATA technology. To address some of the more obvious issues, we have taken two of the new Barracuda SATA-V drives in single drive as well as in RAID-0 configuration and pitted them against the same drive using a parallel interface as well as some well established drives in the field, that is, the IBM 120GXP and the Maxtor D740X-6L. As testbed we used both the ASUS P4G8X (Granite Bay) and the ASUS A7N8X (nForce2) with either the on-board Silicon Image 3112-R controller or else a Silicon Image SATA-Link 3112-A PCI controller card.

Some of our results were predictable, others were strongly influenced by the version of driver used. Needless to say that the latter point goes for the nVidia IDE controller as well as for both Silicon Image interfaces. In the end, we were not prepared for some of the benchmark results we got.

Serial versus parallel cable and connector design. For most users, it is still counterintuitive that the narrow red cable can provide more data throughput than the wide black cable. The same goes for the tiny black SATA connector compared to the large grey IDE connector. The power connectors are similar in size but the traditional white connector appears more solid. Or not?

From a technical standpoint, the main event not only in the storage industry but ramifying into all branches of the PC and server industry has been the transition from the classical parallel IDE or ATA interface to the new serial interface. At present SATA is mostly associated with hard disk drives but both Oak Technologies and Philips have serial optical drive prototypes and suffice it to say that we are already looking at some of the new multi-lense DVDs that will enjoy the benefits of SATA technology.

The Narrow Bus Acceptance Challenge

SATA is still somewhat controversial and introduction of drives into the market is behind schedule. Aside from technical issues, one of the major challenges with respect to public acceptance of SATA technology has been the somewhat counterintuitive notion that a narrow interface using a serial protocol can be faster than a wide parallel bus with a multiplicity of data lines operating in unison or synchronously. Unfortunately, this kind of concept is not just present in the average consumer but also still widespread in the sales personnel in computer retail stores. In other words, if a big cable can't do the job, why should a thin cable suffice?

In short, parallel interfaces are very limited with respect to frequency because of timing skew between the different signals. These skews can be caused by differences in trace length but also by impurities in the conducting traces and further by factors as trivial as nicks in a cable. A different description for skew would be signal delays or phase shift between the different lines. Any serial interface, on the other hand will enjoy the benefit of only a single data line plus reference (or two data lines, in case differential signaling is used). In a full duplex configuration, that is separate I/O channels for reads and writes, a total of four differential data lines is used, however, it is still only two lines per channel. Neither scenario will be subjected to signal skew problems as they incur on a wide bus. Moreover, the paucity of lines allows to allocate a generous amount of conductor to each channel, and thus, warrants optimal transmission characteristics of the connecting media. The electrical characteristics of the cable, together with the low voltage swing-differential signaling protocol hitherto reserved for SCSI are the key factors for understanding the benefits of the Serial ATA interface.

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