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How does it work There are three physical parts to the USB system. These include the host (computer), hubs, and devices. All connectors are one-size-fits-all, so a device can be plugged directly into the host, or into a hub, which in turn is plugged into the host. The USB cable is thin (four wires) and carries enough power for low-power devices, like keyboards and mice. The maximum bandwidth is 12 MBPS, which is shared amongst all devices on the USB network. Since devices are organised in a tiered fashion, not every device needs a direct connection to the host. A device can be plugged into a hub, into another hub, and then the host, thus avoiding a clutter of wires behind the computer. Whenever you plug in a device, the host senses voltage differences in the USB network and proceeds to query (enumerate) the device for type, vendor, functionality and bandwidth required. That device is assigned a unique address ID and co-exists with all other USB devices. Even if two identical devices are plugged in, they will each have a unique address and can be distinguished separately by the computer. Once enumeration is complete, the appropriate device driver is loaded by the operating system and the user will be prompted for the driver disk if necessary. All contention of devices is handled by the host and by the software residing on the host. There is no need to configure interrupt IRQs, addresses, or DMA channels. When devices are detached (unplugged) from the USB network, the host computer detects the detachment, alerts the appropriate application and unloads the drivers. Other than plugging and unplugging the devices there is no user intervention in configuring the devices. How user gains First off, you can simultaneously connect up to 127 devices to your PC, with cable connections reaching five meters in length. This means that the number of devices you can have is not limited to the number of ports at the back of your PC, nor is it limited to the space of your desktop since you can place devices quite far from the host. A standardised plug interface means convenient and headache-free addition of new peripherals. The same plug is used for different types of devices so you don't have to worry about an adapter for the mouse or video camera. Since USB is an industry-wide and royalty-free open standard, everyone can develop USB devices. This ends the need for proprietary interfaces and guarantees cross-vendor compatibility. The most exciting innovations of USB are its Plug and Play features. The inclusion of software and driver requirements as part of the USB specification ensures Plug and Play functionality. Another amazing feature of USB is hot plugging, which means you can plug a device into your machine without turning it off! With serial port-based devices, you can always plug and unplug the cables, although it is not recommended. The PC usually does not know when these attachments and detachments are made and what to do with them. With USB, you can be updating your homepage and decide you want to post up some video clips from your trip to Cancun. All you need to do is plug in your digital camera into a USB port and your computer automatically installs the necessary drivers for it (No need to reboot!). The USB-compliant O/S is so intelligent that it will unload the drivers to save memory when you unplug your camera. Now that's plug and play! Since most of the intelligence needed to manage the USB devices is software based, peripherals are simpler to design and produce, and this efficiency translates into lower costs for the consumer. Near future We have mentioned new input devices that bring the user and the machine closer together. We also talked about easily importing multimedia into our applications. Although we all look forward to these new and creative devices made possible through USB in the near future, we'll probably be seeing more commonplace peripherals ported over to USB. Keyboards, mice, modems, and scanners are among the first to wade USB waters. Soon after, some common devices with new features will appear, such as speakers that can be tuned from an onscreen control panel. A possible development is that iMac (equipped with USB) users may gain access to a larger variety of peripherals, since only a driver rewrite will make a USB device platform portable. Since the personal computer has evolved
from a small business tool to a common information appliance in the
modern household, the demands placed on it in terms of usability have
also changed. Users are less tolerant to problems with installation and
set up. USB is just another step closer to making the personal computer
the ultimate household appliance that will answer your calls and make
your coffee. |
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IN
a day and age where personal computers are used for a myriad of
applications, many new devices have sprung up since IBMs original two
serial port personal computer some 20 years ago. Scanners, portable
hard drives, Zip drives, and force-feedback joysticks are just a few
examples of devices appearing on the desktop. Although attempts have
been made to provide four to eight serial ports on a single PC, there
has been no real standard that gained widespread acceptance. SCSI
seemed to be the solution of choice for many vendors of scanners and
external drives. However, interface cards and devices were expensive
and the standard lacked complete unity. Therefore, many began work on
specifications for new interconnecting solutions, such as IEEE 1394 (FireWire)
and USB.