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What
is USB good for?
USB
for great for attaching medium speed devices to computers. It's
maximum speed of 12 Mbps is fine for low speed devices like keyboards,
mice, or joysticks. It is also well suited for medium speed devices
like floppy drives, cameras, modems, or scanners.
Also,
because it's "hot-pluggable" you can plug devices in
or unplug them safely when you computer is turned on.
Using
either multiple ports on your computer or a hub, you can attach
an almost unlimited number of devices - theoretically up to 128
if you have them.
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What
is "hot-swapping?"
One
of the best features of USB is that it is hot swappable. This
means you can walk up to a computer, plug in a new device using
USB, and use it right away.
Most
connectors on computers can only be plugged in when the computer
is off. This prevents electrical shorts or glitches that can cause
damage. USB doesn't have this limitation.
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What
is "plug and play?"
Plug
and play refers to the ability to use a new peripheral without
going through an elaborate configuration process.
Plug
and play depends on the operating system used on your computer,
Windows 98 and MacOS have a set of basic USB drivers built in
that gives them true plug and play for a wide class of USB peripherals.
Even so, newer types of USB devices may need additional drivers
installed.
USB
is well suited for plug and play operation. No jumpers need be
set or id's selected. There are no interrupt conflicts or other
messy configuration issues involved in using USB devices.
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What is a Hubs?
Most computers have two USB ports. If you need to plug in more than two USB devices you do so by using a hub. A hub plugs into your USB port and provides more than one additional plug. Common hub sizes include four or seven ports.
Many
USB devices have hubs build right into them. Most keyboards have
another USB port in them so you can daisy chain a mouse, joystick,
or other USB device to it.
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Self-powered
vs. powered hubs?
One
important feature of USB is that the cables distribute power as
well as data. This means that devices that use modest amounts
of power don't need separate power supplies. So few big power
cubes at your wall outlet and fewer cords running across your
desk.
Still,
the amount of power distributed over USB is limited. A unpowered
(or self-powered) hub uses some of the power coming to it for
it's own operation, and passes the remainder along to devices
plugged into it. This is OK for small hubs with low power devices
plugged into it. A good example is this is a keyboard with an
powered hub built-in. This has plenty of power for plugging in
a mouse or track pad.
Powered
hubs have their own power supplies and can supply full power to
all the devices that can physically plugged into them. Of course,
you do have an extra wire and power block plugged into the wall.
Some
hubs can operate either way. If they don't have their power supply
plugged-in, they operate as an unpowered hub - with a limited
ability to power additional USB devices. When you plug-in their
power supplied, they function as powered hubs.
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How fast is USB 1.1 and 2.0?
USB 1.1 has a "low speed" mode operating at 1.5 Mbps and a "high speed" mode operating up to 12 Mbps. USB 2.0 can atain speeds as high as 480 Mbps.
Low
speed mode is often used by slower devices such as mice, keyboards,
and joysticks.
High
speed mode is required by faster devices like scanners and printers.
USB 2.0 is primarily used for storage device like large hard disk
drives and CDRW drives.
Today
this speed range places USB firmly in the midrange. SCSI and Firewire
are faster, serial and ADB are slower. A few years from now USB
will undoubtedly be viewed as low speed... USB 2.0 is almost as
fast as current FireWire (except for full motion video) and external
UltrsWide SCSI.
Most
computer with two USB ports place both ports on the same USB bus.
This means that the bandwidth is shared between them. So, if you
have USB speakers on one port, and a printer on the other, the
printer will run slower when sound data is being sent to your
speakers.
New
computers, such as Apple's G4, are using separate USB buses on
each USB port. This means that you can use the full 12 Mbps bandwidth
on each port.
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Can
my computer use USB devices?
This
depends on two things: hardware and software.
Hardware-wise,
you need a USB port in your computer. This can either be built
in (most PC's build in 1999 and Apple's iMac) or from a plug in
card.We offer PCI to USB adapters which can add USB capabilities
to your older computer.
Software-wise
for Wintel computers, you need either Windows 98, Windows 95 OSR
2.1 (although Windows 98 has better USB support than Windows 95),
Windows 2000. For Apple Macintosh computers you need MacOS 8.1
or later.
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How
long can cables be?
Five
meters is the maximum cable length allowed by USB. You can achieve
longer cable runs by inserting a hub every five meters (16 feet).
Companies are also introducing cables with repeaters built into
them to allow longer cable runs.
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Type
A or B / upstream or downstream?
Type
A plugs are the USB output port of a host system or hub. These
are also know as upstream ports. The USB plug in your computer
is a Type A plug. Your typical USB device with a single cable
coming out of it plugs into a hub or host systems Type A port.
Type
B plugs are the USB input ports leading into hubs. These are also
know as downstream ports. They always connect to a Type A, upstream
port, at the other end of the cable.
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How
do I daisy chain my USB devices?
USB
devices are not daisy chained, rather they use hubs to connect
more devices. If you have a single USB port on your computer and
need to use three USB devices, you need to first plug a hub into
the computer. The hub will then have four, or seven (or however
many) ports available for you to plug in additional devices.
Hubs
can be daisy chained, to provide even more USB ports.
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