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USB or Universal Serial Bus

(This page is an Excerpt from the belkin.com web site, they don't say anything about copyright so here it is.)

The Universal Serial Bus (USB)

USB is an open specification defining a significant advance for the attachment of peripheral devices to personal computers. It was developed by a group of industry leaders including Compaq, DEC, Intel, MICROSOFT, NEC, and Northern Telecom. The USB specification includes standardization of connectors and cables, a hub/star topology for the external connection of up to 127 devices, and protocols for automatic device recognition and configuration. USB supports 2 bus transfer rates- a lower speed (1.5 Mbps) for the attachment of low cost peripherals such as joysticks or mice, and a higher speed (up to 12 Mbps) for the attachment of devices that require more throughput, such as communications gear or a digital compressed video camera.

What Operating System?

Windows 95 OSR 2.1 added limited support for USB peripherals, but Windows 98 does a much better job, making USB connectivity alone a valid reason for an operating-system upgrade. In large part the Windows 98 advantage is due to over 3000 bug fixes; and to improvements based on testing. The USB Win32 Driver Model (WDM) and the USB driver interface were tested for a longer period and on a wider selection of devices than was the case for Windows 95 OSR 2.1, in which the WDM was referred to as Version 0.9. Use Windows 98 whenever possible.

USB Basics

USB hubs allow you to hook up multiple devices to your computer via a single USB port, and you can daisy chain hubs for even more ports. Using hubs is simple in theory, but you're more likely to be successful if you understand a little about how the USB bus provides data and power.

The aggregate USB data-transfer rate for a PC is 12 Mbps, approximately the speed of a typical Ethernet LAN connection. The total power supplied via a USB channel is 0.5 amps, or 500 milliamps (ma). The PC's USB controller and internal hub manage the devices, using a step called enumeration, in which each USB device is identified in turn, sharing data bandwidth and power as required.

Power

Belkin ExpressBus (F5U001 & F5U010 )
There are bus-powered hubs available that have no external AC power adapters and draw all power from the PC bus, but if you use bus-powered hubs you limit further connectivity levels (hubs plugged into hubs) and may even preclude using more than one peripheral on a hub. With bus-powered hubs, a single device may take up the total 500-ma load. This is particularly a problem with devices that don't have their own power connectors, such as bus-powered USB digital videoconferencing cameras.

A better idea is to use powered hubs; not only does a powered hub add an AC adapter to plug in, but good ones provide a full 500 ma per port. To determine hub power required, count the USB downstream ports on a hub and multiply by 0.5 amps. Next look on the hub's AC adapter for the amperage rating. A good powered hub would have an AC adapter rated for at least 2.1amps for a four-port hub and at least 3.6 amps for a seven-port hub. Having a bit more than minimal power is even better, to provide the electricity to run LED status indicator lamps. You'll also want to make sure the hub supports per-port switching, a feature that prevents one failed device from taking down the whole chain. Without it, if one device attached to a hub has a short, the whole hub and any further generation hubs and devices will likely lose power. Per-port switching isolates each port and shuts down only the port into which a shorted device is plugged.

Cable Length

Do not extend the distance between segments greater than 5 meters. If you need to go beyond 5 meters use a powered USB Hub (Belkin ExpressBus 4 or 7 (F5U001, Ingram SKU # & F5U010, SKU # 666968).

Installation Issues

Always make sure that USB support in the Computer's CMOS is enabled. To allow keyboards and mice to work at the DOS prompt enable USB Legacy support if available.

Make sure the following devices appear in the device manager for USB support. With these two devices showing you have a successful installation of USB. (Figure 1) If not all occurrences of USB devices should be removed from device manager in both safe and normal modes and then reinstalled.
Figure 1

The information available in the following figure (Figure 2) will assist you in determining what IRQ's are available. This screen can be accessed through the System Start menu, under accessories/system tools.
Figure 2

The Installation process for USB varies by device, but for those peripherals that don't require their own software loaded first, Windows 98 generally recognizes the device identification or type and ask for the Windows 98 CD-ROM. Some USB devices require that you run the included software before making the initial device connection. Normally you connect the device and read the drivers from the installation disks directly.

If you're attaching just one or two USB devices to your PC, you can do so directly; once you've installed each device, you should be able to plug and unplug at will with no problems or surprises. The expansion potential of USB and the growing number of peripherals, however, suggest that most users will end up with more devices on their PCs, which means using hubs to add USB ports.

Cables

One key to success in attaching USB devices is to choose the right cables. Many devices come with attached cables that should be connected directly to PC USB ports or to hubs. Some faster devices such as printers, scanners, drives, and speakers use detachable cables. A detachable cable has a square-end plug (also known as the B connector), which fits into the device, and the more familiar flat USB connection end (also known as the A connector), which plugs into a PC or hub port. As with other peripheral-connection types, the best connection is the one that uses the shortest cable for the job with adequate-gauge wire and shielding. All Belkin USB cables meet or exceed the USB specification.

Because part of the motivation of the USB specification was the need to keep prices low, the specification has precise definitions of the minimum cable gauge per length. Using a longer cable than indicated can cause an unacceptable voltage drop, resulting in unreliable performance or connection failure. The USBIF specifically forbids the use of certain cables and passive pass-through connectors on devices such as keyboards or monitors because of the potential for voltage drop. While some vendors have reported success using these devices, for the most reliable performance do not use cables with a total length greater than 5 meters between devices. Belkin cables (F3U134-06 & F3U134-10) should be used to attain the 5 meter distance between devices and not beyond. Belkin is currently developing cables that will meet the USBIF specification and extend the distance between segments to 15.5 meters.

A wide variety of USB peripherals are now available: keyboards, mice, joysticks and game controllers, printers, scanners, digitizers, digital cameras, video cameras, speakers, modems, network connectors, hard disks, removable storage devices, fingerprint readers, and hubs. The USBIF maintains a list of products on its Web site (www.usb.org). While the earliest devices usually included drivers to work with Windows 95 OSR 2.1, often with mixed results, many of the newer USB peripherals support Windows 98 only. Buyers should be aware that some peripherals with multiple connection ports may purport to support both Windows 95 and Windows 98. On closer inspection they connect via USB only with Windows 98 systems and require another connection--such as a parallel port for a printer or analog connection for speakers--on Windows 95 PCs.

Sharing USB Devices

Although it does not meet the USBIF specification at this time; Belkin's USB manual switch boxes will allow USB devices to be shared. Example the F1B201 will allow 2 PCs to share 1 USB device and the F1B202 can be used for 4 PCs to 1 USB device. Other more complicated configurations can be created using a combination of USB hubs and switch boxes. Remember these have not been approved by the USBIF.

Performance Tweaks

To insure the best possible performance with USB, use high speed devices (Cameras, printers, scanners and zip drives) when possible plugged directly in the computer's USB port. If you really want the best possible performance install multiple Belkin BusPort cards (F5U005) and use each downstream port as dedicated to one device.

Conclusion

The bottom line is that while Windows 95 OSR 2.1 significantly limits the selection of supported peripherals, all compatible devices will work on both native and upgraded Windows 98 test-beds, with no noticeable differences between the native and upgraded operating systems. You will be able to hook up nine devices successfully via one PC USB port and two powered hubs on both systems; more connections are also possible.

Patience will always pay off. When installing a new USB device, the existing devices may sometimes go off-line, but a cold start will be all it takes to power up all of the connected devices. Do run Windows 98. A limited selection of peripherals run under Windows 95 OSR 2.1; for the widest selection of devices and for the best results when attaching multiple peripherals, Windows 98 is required.

Do have your Windows 98 CD-ROM disk handy. You'll probably be asked to insert the CD the first time you install each new peripheral on either USB channel, even if the files or drivers needed are already installed. To save time have the CD ready, or better yet, install the Windows 98 CAB files in a subdirectory on your C: drive if you have room.

Don't use bus-powered or under powered hubs, which can significantly restrict the number of supported peripherals. Instead, use self-powered USB hubs with at least 500 milliamps per channel. Hubs should also feature per-port switching, so one bad peripheral won't shut down all devices on a hub, and LED indicators for device status.

Don't use cables longer than 5 meters, and don't use passive pass-through connectors on monitors or keyboards. While extension cables and connectors are available, significant signal degradation is a risk if you use them.

Do check that previously installed components still work after you install a new USB peripheral. Our testing showed that rebooting the system after installing a new USB peripheral often suffices to get everything working again, but it is common for individual devices to stop working during installation of a new peripheral.