USB Hard Drives and
Personal computers are used
for a wide range of applications and many new devices have been developed since
IBM's original two serial port personal computer some twenty years ago.
Scanners, portable hard drives, Zip drives, and force-feedback joysticks are
just a few examples of devices appearing on the desktop. Although attempts have
been made to provide more serial ports on a single PC,
there is no real standard that has gained widespread acceptance. SCSI seemed to be
the solution of choice for many vendors of scanners and external drives,
however, interface cards and devices were expensive and the standard lacked
unity. Therefore, many began work on specifications for new
interconnecting solutions, such as IEEE 1394 (FireWire) and USB.
USB Hard Drive Interface
The Universal Serial Bus (USB) is the solution touted by seven leaders of the PC
and telecom industry: Compaq, DEC, IBM, Intel, Microsoft, NEC and Northern
Telecom (now, Nortel Networks). Though slower than FireWire (IEEE 1394), USB
still boasts a data rate of 12 Mbps (mega-bits per second) and allows you to
connect up to 127 devices to your PC! It is designed to support modems,
keyboards, mice, 4x – 6x CD ROM drives, joysticks, tape drives, floppy drives,
scanners and printers. In addition, a new wave of peripherals such as
telephones, digital speakers, digital snapshot and motion cameras, data gloves
and digitizers are to take advantage of this exciting and versatile new
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How Does USB Work?
There are three physical parts to the USB system.
These include the host (computer), hubs, and devices including hard drives. All connectors are
one-size-fits-all, so a device like an external USB hard drive can be plugged directly into the host, or into a
hub, which in turn is plugged into the host.
The USB cable is thin (four wires) and carries enough
power for low-power devices, like keyboards and mice. The maximum bandwidth is
12 Mbps, which is shared amongst all devices on the USB network. Since devices
are organized in a tiered fashion, not every device needs a direct connection to
the host. A hard drive
can be plugged into a hub, into another hub, and then the host, thus avoiding a
clutter of wires behind the computer.
When you Plug in a USB Hard Drive or other device, what
Whenever you plug in a device (like a USB hard drive), the
host senses voltage differences in the USB network and proceeds to query the device for type, vendor,
functionality and bandwidth required. That device is assigned a unique address
ID and co-exists with all other USB devices. Even if two identical devices are
plugged in, they will each have a unique address and can be distinguished
separately by the computer. Once enumeration is complete, the appropriate device
driver is loaded by the operating system (O/S) and the user will be prompted for
the driver disk if necessary. All contention of devices is handled by the host
and by the software residing on the host. There is no need to configure
interrupt IRQs, addresses, or DMA channels.
When devices are detached (unplugged) from the USB network, the host computer
detects the detachment, alerts the appropriate application and unloads the
Other than plugging and unplugging the devices, there is no user intervention
in configuring the devices. For more information on
USB Micro Drives and USB Portable Drives, go to
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