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BOOT CAMP 247 (15/10/02)
All About USB
The backsides of most PCs are frightful places and best left
alone once the machine is working smoothly. Fortunately it’s fairly obvious what
most of the plugs and sockets on a PC or laptop do and in general they only
connect to one thing, like the monitor, mouse, keyboard, printer and
loudspeakers but there are other types of socket, generically known as ‘Serial’
ports, which can connect to lots of different things. Two of them, USB and
FireWire, are becoming increasingly important for linking your PC to devices
like printers and scanners and a new generation of electronic widgets that
includes digital cameras and camcorders, web cams, broadband modems, and
personal stereos, to name just a few. These sockets and what they do are well
worth getting to know so we’ll begin this brief series with the USB or Universal
Serial Bus, which is currently undergoing a major revision.
If your PC or laptop was built after 1998 and it uses Windows
98, SE, ME, 2000 or XP then it should have at least one, and probably two USB
sockets. Windows NT doesn’t support USB and don’t even think of using it on PCs
running Windows 95. USB is by far the simplest and now the commonest way of
connecting peripherals to a PC. The plugs and sockets are easy to spot. There
are two basic styles: the flat lozenge shaped ‘Type A’ plug and socket, or
‘Upstream Port’ which you will find on your PC, and the smaller square shaped
‘Type B’ connector or ‘Downstream Port’, which is fitted to most peripherals.
There’s also a Mini USB downstream port connector for pocket-size gadgets.
If you look closely at a USB connector you will see four
pins, two of them (pins 2 & 3) carry data between the PC and peripheral, the
other two are connected to ground (pin 4) and a 5 volt DC supply (pin 1), which
is used to power small devices with a current drain of no more than 100
milliamps. USB cables can be up to 5 metres in length, cable runs can be
extended in multiples of 5 metres using gizmos called ‘hubs’, more about those
in a moment.
One of the main advantages of USB is that it is ‘hot
swappable’, in other words you can connect and disconnect a peripheral without
shutting the PC down. Windows (and the Mac and Linux) operating systems
automatically recognise USB devices and load the appropriate driver software –
assuming it is installed on the computer -- as soon as the connection is made.
If Windows can’t identify the peripheral or find a suitable driver the New
Hardware Wizard starts and you will be promoted to load the appropriate
installation disc.
Another big plus point for USB is that up to 127 USB devices
can be ‘daisy-chained’ together and connected to a single PC; someone tried it a
few years ago and it actually worked! With so many new gadgets coming on to the
market the one or two sockets fitted to most PCs and laptops are woefully
inadequate but it’s easy to add more, using a hub. There are several types, the
simplest and cheapest work like multi-way mains extension sockets and provide
several outlets (usually 4) from a single USB connection. These are really only
suitable for small low-power devices and peripherals that have their own power
supplies (printers etc.). More elaborate ‘powered’ hubs come with a plug-in
mains adaptor so they can be used with used with several USB devices that
require an external supply, like modems, memory card readers and web cams. You
can also get multi-way hubs that live inside the PC, on a card that fits into a
PCI adaptor slot on the motherboard. These are fully powered and work like the
PC’s standard USB sockets.
The USB 1 system, which is the one fitted to most current PCs
carries data at between 1.5 and 12 megabits per second. That is more than enough
for printers, scanners and keyboards but a tad slow for shifting really large
volumes of data around, for storage devices and digital video, for example. To
overcome the speed limitation a new standard was established in 1999, called USB
2 or ‘USB Hi-Speed’. USB 2 is up to 40 times faster than USB 1 and on a good
day, with the wind in the right direction data transfer rates of up to 480Mb/sec
are possible.
New port adaptors are required for USB 2 (now fitted to some
recent motherboards as standard) but it uses the same connectors and is
backwards compatible, i.e. USB 1 devices can be used on a USB 2 PC, but the data
rate of the bus drops to a maximum of 12Mb/sec to accommodate the slower device.
Support for USB 2 is available for Windows ME, 2000 and XP, Microsoft has
decided not to support earlier versions of Windows (98 and SE) but third party
drivers are available from port adaptor manufacturers.
USB is generally very reliable but when things go wrong it’s
usually the fault of the driver software but a surprising number of problems can
be solved by just swapping the plugs
around. On some motherboards the two standard USB sockets can interfere with
each other so it’s advisable to fit a hub if you want to use more than two
devices. However hubs can cause problems in their own right, especially cheaper
unpowered ones so the best way to add extra USB ports to a PC is with a plug-in
PCI adaptor card.
Next week – All about FireWire
JARGON FILTER
BUS
In a computer system an electrical circuit carrying data from
one point to another
DRIVER
A
small program that tells Windows how to communicate with a particular piece of
hardware, like a mouse, joystick or printer
PCI
Peripheral
Component Interconnect - high-speed connector and control system, used on most
recent PCs, also used for sound, video, adaptor cards
TOP TIP
If you ever need to re-install Windows you can save yourself
a lot of time and trouble responding to error messages and prompts by
disconnecting all USB devices before you begin. This includes USB keyboard and
mice, which may not operate until their drivers are loaded (you’ll have to dig
out your old PS/2 keyboard and mouse). If you leave the devices plugged in
Windows will detect them during the latter stages of installation and keep
asking you for driver discs. It’s much easier to install Windows first, make
sure it’s working properly, then you can install your peripheral devices one at
a time.
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