USB Questions and Answers.

Q1: What is USB?

A1.1: USB stands for universal serial bus. Personal computers equipped with USB will allow computer peripherals to be automatically configured as soon as they are physically attached-without the need to reboot or run setup. USB will also allow multiple devices-up to 127-to run simultaneously on a computer, with peripherals such as monitors and keyboards acting as additional plug-in sites, or hubs.

A1.2: USB 1.1 and USB 2 - USB 1.1 is currently (2002) the standard offering. It runs at 12Mbps (megabits per sec, not megabytes per sec!), which is fast enough for many applications, but not ideal for an ethernet adaptor or a hard disk. USB 2 is the latest standard and offers speeds up to 480Mbps, which is fast enough for practically anything. If you want to use USB 2 you must fit USB 2 ports to your computer. USB 2 is backward compatible with USB 1.1, which means you can plug USB 1.1 devices into USB 2 ports - they won't run any faster! You can also plug USB 2 devices into USB 1.1 ports, but of course they will only work at USB 1.1 speeds.

A1.3: USB power - USB not only provides serial data in both directions but also some power. For this reason, many USB devices do not need a power supply, which is a good thing all round. Some innovative devices exploit this feature. For example USB mobile phone chargers and a USB desk lamps are both available - supported by ALL operating systems and no drivers needed!

Q2: Will I need special software to run USB?

A2.1: Operating system - USB is supported by Windows, Apple and Linux operating systems. Windows 98SE and above i.e. ME, 2000 and XP all provide good USB support. MAC OS8.6 and later and Linux kernels 2.4.x and later also provide USB support. Windows 95 and so called 'first edition' Windows 98 do not support USB.

A2.2: Drivers - USB devices are normally provided with device drivers to suit various operating systems, as mentioned above. Some new USB flash drives (portable hard drives which use Flash memory rather than rotating disks) do not require drivers to be loaded. This is known as 'driverless' operation and is available when using Windows ME, 2000 and XP.

Q3: Is USB available on mobile computers in addition to desktops?

A3: USB is currently a key feature on most new notebook computers from leading manufacturers, including Hitachi, NEC, Panasonic, Sony and Toshiba. One great advantage of USB is that it allows notebook users to easily share peripherals.

Q4: What are the best applications for USB?

A4: USB plays a key role in three fast-growing areas: digital imaging, PC telephony and multimedia games. The presence of USB means that PCs and peripherals will work together, with a high degree of reliability, in these exciting new application areas. USB opens the door to new levels of innovation and ease of use for input devices, such as the new generation of "force-feedback" digital joysticks. There are also brand new opportunities for all types of peripherals from printers to scanners to high-speed communications such as ethernet, DSL, ISDN or satellite communications.

Q5: What kinds of USB peripherals can I connect to my PC?

A5: USB1.1 carries data at the rate of 12 megabits per second, which is sufficient for "medium to low-speed peripherals". This broad category includes telephones, digital cameras, modems, keyboards, mice, digital joysticks, some CD-ROM drives, tape and floppy drives, digital scanners and specialty printers. USB's data rate also accommodates a whole new generation of peripherals, including MPEG-2 video-base products, data gloves and digitizers. Computer-telephony integration is expected to be a big growth area for PCs, and USB can provide an interface for Integrated Services Digital Network (ISDN) and digital PBXs. USB2 is much faster, the specification is for speeds up to 480 megabits per second, which is faster than Firewire and suitable for almost any peripheral in a personal computer.


Q6: Will traditional PC serial and parallel ports disappear?

A6: While USB will not replace traditional PC ports overnight, it is expected to rapidly become the preferred means of connecting low and medium bandwidth peripherals.


Q7: How many USB peripherals can I connect at once?

A7: Technically, you can connect up to 127 individual USB peripherals at one time. Due to the fact that some devices reserve USB bandwidth, the practical maximum of devices is less than the theoretical maximum. However, PCI-USB add-in cards provide an independent USB bus to which even more peripherals can be connected.

Q8: How many USB products are being developed?

A8: More than 100 USB products were in the market place in early 1999 with hundreds more expected to arrive later in the year.


Q9: How do I know if my PC supports USB? Where can I get USB ready?

A9: If you're using Windows, download the free USB evaluation utility from http://www.usb.org/. It will examine your PC's hardware and software and inform you of your PC's USB capabilities. As a quick rule of thumb, if your PC was made during or before 1996, it probably doesn't support USB. If it was made during 1997, it probably supports USB. If it was made during or after 1998, it almost certainly supports USB. Note that with some PCs, you may have to connect an adapter to your motherboard so you have a place to plug in your USB peripherals. If your PC has hardware support for USB, but you can't find any USB ports, please take a look at the following section in this FAQ.


Q10: Can I use USB devices with Windows NT or Windows 2000?

A10: NT 3.5 and 4.0 (including service pack 4) do not support USB. Windows 2000 (formerly known as NT 5.0) has full USB support.


Q11: How should I install my USB device?

A11: Assuming you have a PC running Windows, follow these steps:

1. Make sure there are USB connectors on the outside of your PC

2. Make sure that your computers operating system supports USB

3. Run any installation software necessary for your device.

4. Plug in your device.

Q12: What's the deal with low/high power devices and bus/self powered hubs?

A12: You may connect high power devices to self powered hubs only and low power devices to either bus or self powered hubs. High power devices are devices that draw more than 100mA from the USB power line, low power devices are ones that draw 100mA or less. High power devices are typically bus-powered cameras, bus powered hubs. Low-power devices are typically mice, keyboards, joysticks, and any devices that come with their own power supply (also known as self powered devices). Most general purpose hubs come with their own power supply as well and therefore are self powered. A subset of hubs called bus powered hubs gets power from the bus and therefore has the limitation of only supporting low power devices.


Q13: How long of a cable can I use to connect my device?

A13: In practice, the USB specification limits the length of a cable between full speed devices to 5 meters (a little under 16 feet 5 inches). For a low speed device the limit is 3 meters (9 feet 10 inches).


Q14: Why can't I use a cable longer than 3 or 5m?

A14: USB's electrical design doesn't allow it. When USB was designed, a decision was made to handle the propagation of electromagnetic fields on USB data lines in a way that limited the maximum length of a USB cable to something in the range of 4m. This method has a number of advantages and, since USB is intended for a desktop environment, the range limitations were deemed acceptable. If you're familiar with transmission line theory and want more detail on this topic, take a look at the USB signals section of the developers FAQ.


Q15: How far away from a PC can I put a USB device?

A15: With the maximum of 5 hubs connected with 5m cables and a 5m cable going to your full speed device, this will give you 30m of cable. With a low speed device, you will be able to get a range up to 27m, depending on how long the device's cable is. With a straightforward cable route, you will probably be able to reach out 25m or so from the PC.


Q16: I need to put a USB device X distance from my PC. What do I do?

A16: If X is less than 25m or so (see previous question), buy a bunch of hubs and connect them serially with 5m cables. If you need to go farther than that, put another PC, or maybe a laptop, out where you need the device to be and network it with the first PC using something that's intended to be a long-range connection, such as Ethernet or RS-485. If you need to use nothing but USB, consider using USB based Ethernet adapters to hook the PCs together.

Q17: How can I connect two PCs to each other with USB?

A17: You need a specialized USB peripheral known as a USB bridge (sometimes called a USB Data cable or USB to USB adapter) to do this. Mutek Ltd offer a USB Data cable in the USB products section.


Q18: You mean I can't make a direct cable connection like a null modem?

A18: Correct. In fact, if you try this with an illegal A to A USB cable, you'll short the two PCs' power supplies together, possibly destroying one or both machines or causing a fire hazard. Even there were no danger to the machines from the problem with two power supplies, there still wouldn't be any way to get the two PCs talking to each other, since USB doesn't support that particular kind of communication. A reasonably priced solution to handle this need is the a USB Data cable.


Q19: What if I want to network a whole bunch of PCs together with USB?

A19: If you need to connect just a few machines, USB bridges and a hub or two will work. USB was not designed to be a LAN, however, and there are certain safety hazards associated with trying to use USB with large numbers of PCs. There's also a large performance penalty compared to a real LAN. If you need a LAN, use a technology intended to be used as a LAN, such as Ethernet.