The Need for Speed for External Storage - Where eSATA Came From
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eSATA’s differences from SATA are what you would expect for a connection that is supposed to take place outside your computer case: the connectors are a little different so they can handle the wear and tear of regular use, and they carry a stronger signal for longer distances (two meters as opposed to the one meter of regular SATA). In addition to a special cable, since most PC motherboards do not yet have an eSATA connector, it requires an additional card for the system.
eSATA is of course an outgrowth of SATA, which replaced ATA (retroactively named parallel ATA). As with eSATA’s advantage over USB, SATA's displacement of PATA has been due to the issue of speed. Parallel ATA transferred data in parallel; it literally pushed it through a number of parallel wires in a cable. This point is obvious just from looking at a parallel ATA cable. If you want to increase the data transfer rate, you can add more wires or increase the speed of the lines – but there are limits. The signals have to stay synchronized, and whatever you do, that’s a complicated juggling act.
SATA, which stands for serial ATA, did away with that problem. The signals in the lines don’t have to be synchronized because chips at either end of the connection sort out where everything goes. Again, this is pretty obvious from looking at a SATA cable, which is a lot thinner than a PATA cable. Since the signal doesn’t have to be synchronized, SATA can transfer data at higher speeds than PATA. In a market progression we’ve seen many times before, the newer technology looks set to replace the older one. In fact, market intelligence company iSuppli reported that shipments of SATA hard drives this quarter just started exceeding shipments of PATA hard drives.
So how fast is a SATA connection? The current generation provides an actual data transfer rate of 2.4 Gb/s, or 300 MB/s. In this case, we’re talking about megabytes, not megabits as we were for USB drives. To compare apples to apples, typical transfer rates for USB 2.0 range around 40 MB/s, or nearly an order of magnitude slower than SATA. Even faster speeds are on the horizon for SATA. The SATA-IO (Serial ATA International Organization) is planning a 6.0 Gb/s standard. While current hard drives cannot operate quite that fast, solid-state drives might be able to take advantage of the speed boost. A connection that operates that quickly would also be useful if you have multiple drives connected to one SATA port.
Next: eSATA’s Hurdles >>
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