Frequently Asked Questions
Q1:How fast is USB?
A1: High speed USB 2.0 products have a design
data rate of 480 Mb/s.
Full speed USB 1.1 devices signal at
Low speed devices use a 1.5Mb/s
Q2:How does this compare to other connections used with PCs and workstations?
A2: Here's a quick list of the maximum transfer
rates for various connections in megabits (Mb) and megabytes (MB) per second:
|standard parallel port:
|ECP/EPP parallel port:
|SCSI-2 (Fast SCSI, Fast Narrow SCSI):
|Fast Wide SCSI (Wide SCSI):
|Ultra SCSI (SCSI-3, Fast-20, Ultra Narrow):
|Wide Ultra SCSI (Fast Wide 20):
|Hi-Speed USB 2.0:
|Wide Ultra2 SCSI:
|Wide Ultra3 SCSI:
|FC-AL Fiber Channel:
The fastest connection commonly found on PCs is UltraIDE, which is used for
hard drives and CD-ROMs
Q3: So which is faster, a
USB peripheral or a serial/parallel/SCSI/1394/etc. one?
A3: This depends on what the peripheral is and
how it's made. For example, a USB keyboard won't let you type any faster than a
normal PS/2 keyboard because your typing speed is limited by how fast your
fingers can hit the keys, not by the speed of the keyboard's connection to the
PC. Similarly, devices like printers and scanners may be able to run faster on
USB than they can with a standard parallel connection, but only if the print
head or scan engine can keep up with USB's higher data rate, which is not
necessarily the case. On the other hand, USB makes possible peripherals that
were impractical with earlier connections, such as video cameras and ADSL and
Q4: Can I use game port,
serial, parallel, or PS/2 devices on USB?
A4: These devices use different electrical
signals than the ones used for USB, so you can't plug them into USB directly.
However, a variety of manufacturers make USB devices that will convert game
port, serial, parallel, or PS/2 devices into USB signals. With these, you can
actually attach many more non-USB devices to your PC than you could without USB.
Note that some devices support multiple connections to the PC, and therefore
come with special adapters that let them connect to USB or another port. These
adapters don't perform any signal translation, so nothing will happen if you
take one of these adapters and put it on another device that doesn't support USB.
Q5: Will using a USB to
serial or parallel adapter free up interrupts on my system?
A5: Yes, but you'll probably have to manually
disable the serial or parallel ports in your BIOS before something else can use
Q6: What about EIDE, SCSI
and network adapters?
A6: USB to EIDE, SCSI-2, and Ethernet adapters
are also made.
Q7: I'm planning to add USB
to my system, buy a system with USB, or buy a USB device. What should I look
A7: The USB-IF does not endorse specific
products, but you can search the USB-IF's product
list to find out what's out there. As always, however, it's wise to look for
products made by manufacturers who have invested the time and effort to required
to build reliable products. In particular, many people have become quite
frustrated with USB devices that are only supported under one class of host
controller or with motherboards which, while having the chip needed for USB,
didn't come with any USB ports to plug USB devices into. As a result, the USB-IF
does suggest looking for USB devices that will work with any host controller
(both UHCI and OHCI) and for motherboards which come with USB ports.
Q8: So how does USB compare
A8: While the two serial buses seem similar,
they are intended to fulfill different bandwidth and cost needs. 1394 can move
more data in a given amount of time, but is considerably more expensive than USB
due to its more complex protocol and signaling rate. Applications that are best
suited for 1394 are disk drives, high quality video streams and other high
bandwidth applications; all higher end consumer devices. USB is appropriate for
middle and low bandwidth applications such as audio, scanners, printers,
keyboards, and mice.
USB and 1394 are complementary technologies. 1394 is for devices where high
performance is a priority and price is not, while USB is for devices where price
is a priority and high performance is not.
The above information was found at http://www.usb.org/faq/ans2.html#q1
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