USB 3.0 vs. eSATA: Is faster better?

While USB 3.0 is good, it's not as simple as "Whoever's the fastest wins." Let's take a closer look at these new and improved ports on our PCs.

Up-to-date computers now include external ports that, in theory, can handle data at rates of up to 5 Gigabits per second. But which is better?

If you've been in the computer business for any length of time you can probably painfully remember when serial RS-232 ports could barely handle 28 Kilobytes per second. And, adding insult to injury, the standard was loose enough that you could have 'compatible' devices that you could never physically connect. How things have changed! Now, eSATA can handle 300 MBps (MegaBytes per second) and USB 3.0 can wheel and deal up to 625 MBps.

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So that makes USB 3.0 better right? Well, while USB 3.0 is good, it's not as simple as "Whoever's the fastest wins." Let's take a closer look at these new and improved ports on our PCs.

ESATA (External Serial Advanced Technology Attachment) is the external version of the technology, SATA, that your computer is likely already using for its hard drive. While SATA and eSATA are both older than USB 3.0, its proponents would still claim that it's better than USB 3.0.

They can make this argument because the most common use for eSATA is for external hard drives. Internally, these drives are still using SATA even if you're connecting to these devices with USB or FireWire on the outside. Thus, the argument goes, these devices must use a bridge chip to translate from the ATA protocol to USB or the FireWire IEEE 1394 protocol.

There are two ways to do this. The first is to encapsulate the SATA protocol-borne data into USB or FireWire. The other is to actually convert the data into one of the external data transmission protocols. In either case, this requires extra steps and processing, which slows down the effective throughput.

Various benchmarking tests support this claim. In particular, eSATA has clearly been shown to be faster than USB 2.0.

That was then; this is now.

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Today, USB 3.0's SuperSpeed 5 Gbps (Gigabits per second) is more than ten times faster than USB 2.0's top theoretical speed of 480 Mbps (Megabits per second). In addition, USB 3.0 supports asynchronous data transfers, which means that, unlike USB 2.0, it doesn't need to wait to poll a USB device every time it wants to start shipping data one way or the other.

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In addition, USB 3.0 includes a new transfer method called Bulk Streams. With Bulk Streams, USB now supports multiple data stream transfers. The net effect of this is that the protocol will do much better with huge data transfers such as those required by viewing an HD movie that's residing on an external hard drive.

Still, on those same external drives, USB 3.0 must deal with the SATA to USB protocol conversion slowdown. So, who wins when it comes to raw read and write speeds? We still don't know.

I did, however, run some rough benchmarks to get an idea of what we're dealing with. For my devices I used a Western Digital My Book Studio Edition II 1TB 7,200 RPM external hard drive with its eSATA port and ran it against a Western Digital My Book 3.0 with a similar drive inside. I attached these to a Gateway SX2802 PC with a 2.5GHz Intel Core 2 Quad Q8300 CPU and 6GBs of DDR2 memory. On this system I was running Windows 7 Ultimate. To enable it to handle USB 3.0, I installed a StarTech 2 Port PCI Express SuperSpeed USB 3.0 Card Adapter.

With this setup, USB tends to be about 20% faster than eSATA at reads, while eSATA was about 20% faster at writing data to the disk. While I make no claims for these to be definitive benchmarks (I used the freeware Crystal DiskMark 3.0 program for my tests), I do think the results indicate what you can expect to see from today's eSATA and USB 3.0 drives.

In both cases the real world results were quite a bit slower than their theoretical bests. With reads, my USB drive averaged 90 MBps, while the eSATA drive came in at 75 MBps. When it came to writing to the disk eSATA still processed data at 75 MBps while the USB drive dropped to 62 MBps.

This kind of difference between real world and theoretical results is quite common. Nothing in your office or home, or even the test bench, will ever run as fast as its design specifications call for.

That said, I was surprised to see USB 3.0 do as poorly as it did. Mind you, it's still much faster than USB 2.0 and somewhat faster than eSATA in data reads. I had expected better from it. I strongly suspect that as USB 3.0 devices and drivers mature, it's speed will significantly improve.

USB 3.0 does have some other advantages over eSATA. For example, like USB 2.0, you can power devices through a USB 3.0 connection, while you'll need another power connection for external eSATA devices.

In addition, USB 3.0, which can handle up to 50% more power than USB 2.0, should be thriftier with energy than 2.0. Alas, it's not. As Brian Nadel reported in ITworld's sister publication Computerworld, current USB 3.0 implementations will drain your laptop's battery faster than their equivalent USB 2.0 devices. Again, the next generation of devices and drivers should handle this better.

Another noteworthy point is that while USB 3.0 is backwards compatible with USB 2.0 cables and devices, you can't use a USB 3.0 cable with a USB 2.0 or earlier device. In addition, you can't use any USB 3.0 device with a USB 2.0 cable. That's because while the flat USB Type A plug, the one that goes into your PC, is compatible with USB 2.0 ports even though it has an extra pair of connectors, the other end is a different story entirely. The Type B plug, which is the one that you use to connect devices to the computer, comes in two different varieties. Neither of these will fit into a USB 2.0 B port.

So, what should you do? If I were you, I'd stand pat for now. USB 3.0 is the wave of the future. Later this year, as the technology matures, USB 3.0 devices should be consistently faster than today's eSATA devices, but we're not there yet.

In addition, for now, you'll still pay a premium for USB 3.0 devices, boards with USB 3.0 ports, and even PCs with USB 3.0 built-in. Towards the year's end though USB 3.0 will become the default on almost all PCS and peripherals. Much as I like USB 3.0, I don't see any reason to hurry up and adopt it today. I'd advise you to wait too.

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