ad info

 
CNN.com  technology > computing
    Editions | myCNN | Video | Audio | Headline News Brief | Feedback  

 

  Search
 
 

 
TECHNOLOGY
TOP STORIES

Consumer group: Online privacy protections fall short

Guide to a wired Super Bowl

Debate opens on making e-commerce law consistent

(MORE)

TOP STORIES

More than 11,000 killed in India quake

Mideast negotiators want to continue talks after Israeli elections

(MORE)

MARKETS
4:30pm ET, 4/16
144.70
8257.60
3.71
1394.72
10.90
879.91
 


WORLD

U.S.

POLITICS

LAW

ENTERTAINMENT

HEALTH

TRAVEL

FOOD

ARTS & STYLE



(MORE HEADLINES)
*
 
CNN Websites
Networks image


USB for me... USB for you

Image
Network World Fusion

March 15, 2000
Web posted at: 8:24 a.m. EST (1324 GMT)

(IDG) -- Despite the explosion of PCs with Universal Serial Bus (USB) support, Gearhead has been intrigued by how little people know about this new technology. Indeed, Gearhead must admit that our own knowledge was a little sketchy, hence this column.

USB came about because of the need to develop a workable, simple-to-use and low-cost external expansion bus for PCs. This need arose because, although the Peripheral Components Interconnect (PCI) bus solved many performance and compatibility problems that had plagued the old Industry Standard Architecture bus, difficulties related to opening the case to add or change an expansion card and then reconfiguring the system remained.

  MESSAGE BOARD
 

Furthermore, while PCI made the Windows Plug-n-Play system possible, it didn't guarantee that Plug-n-Play worked (hence the other term for Plug-n-Play: Plug-n-Pray).

USB was built around a serial bus (parallel busses are expensive) and designed to allow dynamic configuration. This means that add-on components can be "hot-swapped" (added and installed or removed and uninstalled while the system is running and without rebooting - now there's a step forward).

MORE COMPUTING INTELLIGENCE
IDG.net   IDG.net home page
  USB set-up at a glance
  Music in the key of USB
  Top 10 graphics boards (March 1999)
  Revamping the home computer
  Reviews & in-depth info at IDG.net
  E-BusinessWorld
  Year 2000 World
  Questions about computers? Let IDG.net's editors help you
  Subscribe to IDG.net's free daily newsletter for network experts
  Search IDG.net in 12 languages
  News Radio
  * Fusion audio primers
  * Computerworld Minute

USB uses a master-slave design with the PC acting as the master and controlling the flow of all traffic. Such a design means that slave devices (peripherals) can be less expensive and simpler. Power can also be supplied to USB slave devices through the USB interface, again simplifying the design of peripherals and improving usability. In a USB system, there are four types of devices: I/O devices, hubs, compound devices and composite devices.

An I/O device is the piece of equipment you want to connect to your PC: a modem, keyboard, mouse, scanner, speakers, etc. A USB system can support up to 126 devices. In Gearhead's experience, a few devices (two or three), will operate just fine, but don't push your luck, particularly if your processor is less than a Pentium II.

Hubs connect multiple USB ports to allow a number of USB slave devices to communicate. Hubs can be cascaded to a depth of five levels and here's where choosing the right type of hub can be crucial: If you use a self-powered hub, the USB specification says that 500 milliamps (mA) will be supplied to each connected device or hub. If the hub is self-powered, then only a total of 500 mA will be available to all connected devices. As the hub itself will count as one device, the true total available for all attached devices will be only 400 mA.

As each port demands 100 mA, other hubs that are connected to an unpowered hub will have to be self-powered if they are to function (while cascaded unpowered hubs might work, devices connected to them might not work even if the devices are, in turn, self-powered). In real life, this can be incredibly confusing to end users and support staff.

Compound devices are peripherals that also offer hub functionality: USB-enabled monitors are a good example. Composite devices are the over-achievers of the USB world - they are devices that combine several input/output functions in one peripheral. For example, a keyboard with speakers or combo toaster/MRI scanner (just kidding, Gearhead knows of no such product).



RELATED STORIES:
A look at FireWire and USB
February 10, 2000
Color-coordinated drives due for iMac
January 5, 2000
USB bonanza! Over 15 controllers add to your gaming pleasure
November 19, 1999
USB breaks speed barriers
October 19, 1999

RELATED IDG.net STORIES:
USB set-up at a glance
(Macworld)
Revamping the home computer
(PC World)
USB mouse attack
(Macworld)
Music in the key of USB
(Macworld)
Joysticks for serious gamers
(GameProWorld.com)
Universal port replicator ready to ship
(Infoworld)
The Ten Commandments of installing upgrade cards
(PC World)
Top 10 graphics boards (March 1999)
(PC World)

RELATED SITES:
USB.org
Linux USB
allUSB - USB product news and information

Note: Pages will open in a new browser window
External sites are not endorsed by CNN Interactive.

 Search   

Back to the top   © 2001 Cable News Network. All Rights Reserved.
Terms under which this service is provided to you.
Read our privacy guidelines.