Dan Warne23 April 2007, 7:13 AM
Intel is now working on the SATA 3.0 standard that will provide up to6 gigabits per second of bandwidth. We asked Intel why on earth the world needs yet again another speed boost in the drive interface: surely we need faster drives first?
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Intel is currently in the throes of working out the tech specs for SATA 3.0, which will deliver a rather staggering 6Gbit/s of throughput.
 Knut Grimsrud: hair maketh the man |
I took the opportunity to ask Intel's SATA guru Knut Grimsrud why on earth we needed a third generation SATA standard when we were nowhere near close to saturating the link speed of SATA 1.0, with today's hard disks.
For a start, Grimsrud explained, there's a common misconception out there that SATA provides 1.5 gigabytes per second. People naturally assume that if their hard drive peaks at 100 megabytes per second of throughput, then there's 1.4 gigabytes of free bandwidth on the SATA link.
In fact, SATA is described in megabits per second, while hard drive throughput is described in megabytes per second.
"Serial interfaces commonly represent their signalling speeds in terms of the bit-rate since the data is transmitted a bit at a time. The first-generation Serial ATA interface has an interface transfer rate of 1.5Gbps (gigabits per second) which translates to 150MB/s (megabytes per second).
"In most serial interfaces the data is encoded in such a way that you end up transmitting 10 bits of signals down the wire for every byte, hence you divide by 10 to get the transfer rates in bytes (instead of dividing by 8 like you would expect)," Knut explained.
"The second generation Serial ATA signalling speed is 3Gbps (which corresponds to 300MB/s) and we are now in the process of developing the specification for the third generation signalling rate which will be 6Gbps (which corresponds to 600MB/s)."
Two reasons you'll want more SATA bandwidth
Knut says there are two key reasons we'll need more SATA bandwidth sooner rather than later.
1. Flash is fast.
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"Flash-based solid state drives have the potential for providing higher transfer rates than mechanical disk drives.
"There have been a number of solid state drive announcements from various suppliers and while the performance characteristics of those drives vary from one
supplier to the next, there appears to be an emergence of solid state drives that have the potential for delivering transfer rates that are comfortably higher than mechanical drives.
"Based on the ONFI [Intel's new open standard for flash interfaces, designed to take over from the plethora of manufacturer-specific flash interfaces in use] work we're doing for the raw flash itself, it appears that with sufficient parallelism that fairly high transfer rates can be realized.
"Today's flash components have an interface that supports transfer rates of around 40MB/s, but most solid state drives include a large number of these devices, so depending on the architecture, higher transfer rates can be reached by running the chips in parallel.
Put simply: the fully flash-based drives that will start hitting laptops within the next few years are like giant RAID systems in a very small case.
2. SATA port multiplication
A little-known feature of SATA (particularly because it has been implemented inconsistently between SATA chipset manufacturers) is "SATA port multiplier", where it's possible to connect more that one drive to a single SATA interface.
You may not need that inside your desktop PC which comes with four or more discreet SATA interfaces anyway, but laptop owners may very well welcome the opportunity to connect more than one device to a single external SATA (eSATA) interface.
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The bad news is that there's no easy way -- at this stage -- to tell whether your computer supports SATA port multiplier. According to Knut, "There is no direct visual indication that a particular SATA (or eSATA) port provides support for port multipliers.
"This feature is a function of the supporting platform (SATA controller and supporting drivers), and there is no direct visual inspection that indicates this. For the products I'm aware of, support for this feature is something that appears on the feature-list for the product. This is also true for several other Serial ATA features, such as NCQ support."
When will we see more eSATA?
 An external drive with an eSATA port |
I also asked a supplementary bonus question to Knut -- when will we start to see eSATA on more laptops for full-smoking-speed connection of external hard drives?
"eSATA availability has been fairly limited to date and Intel's chipsets did not provide direct support for eSATA.
"The latest Intel chipsets do provide direct support for eSATA and as a result I expect the availability of directly supported ports will increase.
"My impression is that eSATA ports might be more common in the docking station than on the laptop itself, but this is obviously up to the system designers," he said.
Dan Warne attended Intel Developer Forum Beijing as a guest of Intel.