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A way to connect devices to computers.
Very common for printers, scanners, PDAs etc. For
video needs, FireWire/iLink is prefered. |
USB 1.1
Short for Universal Serial Bus
An external bus that is beginning to replace parallel and serial ports.
With a maximum transfer speed of 12 Mbps (megabits per second), USB is
designed for low- to mid-speed peripheral devices (such as keyboards,
mice, printers, joysticks, and modems) whereas more bandwidth-intensive
devices (such as digital video cameras and storage devices) use the IEEE
FireWire standard. The main advantage of USB over traditional ports is
that it offers easy expandability; you can daisy chain up to 127 devices
(far more than the number of devices supported by traditional ports).
All USB devices support plug-and-play and hot plugging. The computer automatically
recognizes any USB device as soon as it's plugged in or added to the chain.
Desktop computers that support USB typically have two four-pin USB ports
(one for a keyboard and mouse daisy chain, the other to daisy-chain all
other USB devices). USB was introduced in computers in 1997 and has received
a boost from Windows 98, which offered better support for the standard
than Windows 95. Macintosh computers support the USB standard. The iMac,
for example, has no serial or SCSI ports, only USB ports.
USB 2
USB 2.0 extends the speed of the connection from 12 Mbps on USB 1.1 up
to 480 Mbps on USB 2.0, providing an attachment point for next-generation
peripherals which complement higher performance PCs and user applications.
USB 2.0 is both forward and backward compatible with USB 1.1. USB 2.0
uses the same cables and connectors as USB 1.1. USB 1.1's data rate of
12 Mbps is sufficient for many PC peripherals such as telephones, keyboards,
mice, digital joysticks, floppy drives, digital speakers, and low-end
printers. These peripherals will continue to operate with no change in
USB 2.0 systems.
The higher bandwidth of USB 2.0 will permit PC peripherals with more functionality,
including higher resolution video conferencing cameras, next generation
scanners and printers, fast storage units, and faster broadband Internet
connections. Time to download a "roll" of digital photos will
be changed from a few minutes on USB 1.1 down to a few seconds on USB
2.0. As with USB 1.1, USB 2.0 is expected to eventually be in industry
chipsets. Once these chipsets reach high volume, it is expected that USB
2.0 will be about the same cost as USB is today. Because of this, USB
2.0 is expected to supersede USB 1.1, which is already a ubiquitous connector
on PC systems today. To satisfy the needs of power-sensitive applications
such as notebook computers, USB 2.0 will provide the same power-management
mechanisms as USB 1.1 to allow aggressive management of I/O power consumption.
This is expected to allow USB 2.0 to find use even in demanding low-power
systems.
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