Sarasota PC Monitor
Tech Talk(6/98)
The Universal Serial Bus
by Brian K. Lewis, Ph.D.*
Member of the Sarasota Personal Computer Users Group, Inc.Anyone who has been around PC's for any length of time realizes that one built-in problem is the scarcity of serial or communication ports. When IBM first designed the PC, they decided that no one would ever need more than two serial ports at a time. (Just like the idea that 640K of RAM would always be more than necessary.) So the PC was designed with four serial ports, but only two were available simultaneously. That was because they assigned only two interrupts (IRQs) to the four ports. With the PC-DOS or MS-DOS operating system, this scheme worked, to a degree. About the only peripherals using serial ports then were some printers and modems.
Then came the mouse and Windows. Mice were designed to run off a serial port and required constant communication with the port. So you put the mouse on one port with its own IRQ. The printer and the modem could then share an IRQ and be assigned two different port numbers. As the serial printers disappeared, it looked like the IRQ problem was solved. However, then came network cards for LANS, cable modems, digital cameras, drawing boards, joysticks, etc. Though the total number of IRQs was increased to 15 from the original eight, the serial port problem remained.
Another problem with serial ports was a decided lack of speed. In serial ports data is sent one bit at a time. The first ports were limited to 9600 bits per second. The newer ports can handle 115K bits per second. That's a lot faster, but, still not fast enough.
Similar problems are occurring with the parallel ports. After all, these were designed to connect just to your printer. However, now we have tape drives, removable drives and scanners that all want to be connected to your parallel port. If you have a printer that uses bi-directional communication with your computer, adding another peripheral to your parallel port may cause problems with both the printer and the new device. You can sometimes add a second parallel port. However, you may also find that the new parallel port won't work. Sound cards frequently grab the IRQ normally used by a second parallel port.
Obviously, something had to be changed. If you have purchased a new Pentium class computer within the past year, it probably included a new hardware item called a USB port. Microsoft, Intel and Compaq, in cooperation with other manufacturers have developed the Universal Serial Bus as a replacement for the current parallel and serial ports.
Although these ports have been available on computers for at least a year, there has been almost no hardware available to take advantage of them. Occasionally the ports exist on the motherboard, but without any external connectors. Part of the reason for the delay in producing peripheral equipment to connect to the USB has been that Windows 95 does not support the USB. That meant that any manufacturer would have to provide software that would allow the computer to recognize and work with the peripheral. Well, that scenario is about to change. Windows 98 has support for the USB functions.
So what advantages will USB offer to users? Using a single cable, a USB port will allow you to connect your monitor, a keyboard, mouse, drawing tablet, modem, scanner, joystick, printer(s), telephone, to your computer. This is done by daisy-chaining each component or connecting to a multiple port box. In fact, you can link up to 127 devices to a single port on your computer, provided the total length of the connection is not longer than 15 feet. Compare that to the current rats nest of wires you can find behind every computer!
Another advantage of the USB is SPEED! The USB has two data speeds. It uses 1.5 million bits per second for slow devices like keyboards, mice and joysticks. It has a 12 million bits per second speed for monitors, printers, scanners, modems, removable drives, etc. The Windows 98 Plug and Play system is supposed to allow you to add or remove devices from the chain without having to turn off the computer. The operating system is also supposed to be able to detect the change and automatically load or unload the necessary drivers. Please recognize that I have not worked with the USB and therefore don't know how well this system will operate. Still, for the most part, the current Plug & Play works with hardware designed for it.
The next question is, when will the peripherals that can use the USB be available? Well, some of them are already here. I have seen ads in the trade magazines for monitors with USB ports and cables. Some mail order catalogs have keyboards port devices available now. I suspect that once the Windows 98 is released there will be an increasing number of devices available that can take advantage of the USB ports on your computer. Considering the added speed and convenience, I would not be surprised to see Zip drives and their competitors come out with USB connections. The same could be true of the scanner manufacturers. Certainly a USB connection would be faster than most SCSI connections without the cost of the SCSI board. It will take some time for the peripheral manufacturers to catch up on this. My speculation is to look for items to show up in time for the Christmas market.
Microsoft is also rumored to be working on an adapter cable which would enable current serial or parallel devices to be connected to the USB port. That would extend the life of your current peripherals. The USB is one major improvement in Windows 98 whose benefits will not be obvious immediately. In time, I think users will find it a definite asset. So now that you know what your USB can be used for, keep your eyes open for further developments in this area.
*Dr. Lewis, a former university & medical school professor, is currently a computer consultant and part-time computer instructor for Sarasota County Technical Institute. He is available, on a fee basis, to help you with your home or business computer problems. He can be reached via e-mail at bklew@worldnet.att.net or voice mail at 941/925-3047. :
Copyright 1998. This article is from the June 1998 issue of the Sarasota PC Monitor, the official monthly publication of the Sarasota Personal Computer Users Group, Inc., P.O. Box 15889, Sarasota, FL 34277-1889. Permission to reprint is granted only to other non-profit computer user groups, provided proper credit is given to the author and our publication. We would appreciate receiving a copy of the publication the reprint appears in, please send to above address, Attn: Editor. For further information about our group, email: admin@spcug.org/ Web: http://www.spcug.org/
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