Can a 5 year old PC read USB3 external HDD ?

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I guess not.
The hardware standards are NOT backwards compatible?
In this 3rd-world loacation I can get Verbatim 1T HDD: USB3
for slightly more than a Toshiba 500GB: USB2 & 3.

IMO the 1T capacity is absurd, but I prefer the bigger
physical-dimensions, than the minature type, because
it must be more reliable.  OTOH Toshiba is a good make.

When did USB3 come in, while I was sleeping?


Re: Can a 5 year old PC read USB3 external HDD ? wrote:
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USB3 has been around for a while. The first chip to have
it, was a NEC USB3 chip. It made a debut on some $25 PCI Express
cards you could plug into any PCI Express computer.

One of the last places to get USB3, was integrated into an
Intel chipset. That only arrived this year. Motherboards
for the last couple of years, needed to have a separate
chip (like the NEC) soldered to the motherboard, to add


You can see some pictures here.

The data cable for it, illustrates some interesting points.

It has a total of nine contacts. Four contacts plus ground shell,
is the traditional USB2/USB1.1 interface side. The new part
is an additional five signals. It consists of a TX pair, an
RX pair, and a ground signal between groups. The TX pair and
RX pair are similar in concept to the TX and RX pairs used
on SATA or PCI Express slot connectors. They are low voltage
differential interfaces, running at gigabits per second.

Both interfaces function at the same time. When you plug in the
full stacked connector, all nine connections are completed.
The USB2 and USB3 wake up at the same time. But via negotiation,
the hardware eventually only sends messages on one of the two
interfaces. If only the USB2 pins are hooked up, the device will
use USB2 (30MB/sec) disk transfers. If both USB2 and USB3 pins
are connected, then the device can transfer at the faster rate
of USB3.

Practical transfer speed is around 200MB/sec. That's the last
disk enclosure benchmark I saw, and I don't know if any
further progress has been made or not. This is sufficient
bandwidth for even the fastest rotating hard drive (at 180MB/sec).
But there are quite a few SSD drives, where the interface would
not be fast enough. The USB3 would then limit the transfer
rate. Still, this is a great improvement for doing backup
on computers, because the USB2 cable no longer "holds back"
the potential transfer rate of the hard drive. Few people
(yet) use SSDs as backup devices. Rotating hard drives
are so much larger, that it makes sense to continue to use
them for doing backups.

The theoretical best case we could expect for hard drive storage,
is somewhere around 336MB/sec, according to the calculations
here. But this has not been demonstrated on actual hardware.

USB3 has also been used for video capture devices, so it is used
for more than just hard drives. And you might not expect to
see every kind of USB device, take advantage of the higher
speed. Some things don't really need the speed (like a USB keyboard
for example). You wouldn't expect to find USB3 pins on a USB keyboard
or USB mouse.


With regard to the subject of your post "Can a 5 year old PC..."
the answer is yes, if the PC has PCI Express slots. You can
plug in an adapter card.


Re: Can a 5 year old PC read USB3 external HDD ?

If you plug the usb3 cable into the usb2, win 7 will inform you that you
can get more speed if you use the proper socket. [I did this by mistake
and made the discovery.] It turns out the standards have significant
backwards compatibility. Per the wiki:

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A USB 3.0 Standard-A receptacle accepts either a USB 3.0 Standard-A plug
or a USB 2.0 Standard-A plug. Conversely, it's possible to plug USB 3.0
Standard-A plug into a USB 2.0 Standard-A receptacle. The Standard-A is
used for connecting to the computer port.

The peripheral side of the usb3 cable is pretty odd looking. It looks
like two connectors. But the computer side looks like a stock usb
connector except for the color. Late at night, you can easily pick the
wrong socket.

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