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





In a computer system an electrical circuit carrying data from one point to another



A small program that tells Windows how to communicate with a particular piece of hardware, like a mouse, joystick or printer



Peripheral Component Interconnect - high-speed connector and control system, used on most recent PCs, also used for sound, video, adaptor cards 




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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