While USB is great for the reasons explained earlier, there are several things you need to be aware of in order to use USB devices successfully and to avoid damage to your computer equipment or malfunction of the devices.
In order to use more than one or two USB devices to your PC, you need a USB hub. You can combine multiple hubs to cover all your USB port needs. Most USB hubs have 4 or more ports and cost between $20 and $40. There are two types of hubs: unpowered and powered. To understand the difference, you need to know that USB devices still need power in order to operate. Some devices like keyboards and mice only need a very low amount of power, which they get from the USB port through the motherboard. Other USB devices, however, need a lot more power, such as printers and scanners. If they would use the USB port as their sole power source, it would drain too much power from the motherboard and could lead to flaky system behavior all the way to system failure. For that purpose, high-power USB devices come with their own separate power source, usually an AC adapter. If you buy a USB hub to connect multiple USB devices, even if they are low-power ones, you should purchase a powered USB hub, meaning a hub that comes with its own AC adapter and therefore supplies all USB devices with power from its own source instead of draining it from the computer and putting an additional load on the power supply.
There are only certain operating systems that offer support for USB devices. You won’t be able to use USB with DOS, Windows 3.1 or Windows NT 4 or the original version of Windows 95. While Windows 95b and c offer USB support, it is not very reliable and often does not work at all. Also, a lot of times the installer for software used by USB devices will first check to see if you have an OS that supports USB and refuses to install if it does not find a qualifying OS. You need to have either Windows 98, Windows Millenium Edition, or Windows 2000 in order to successfully use USB. Most newer distributions of Linux offer USB support as well but check first to make sure. The reason for this is that the OS needs to be able to support and use the USB port. The drivers you install for each device are solely for the device itself and cannot add USB support to the OS.
While USB is hot-swappable, meaning you can connect and disconnect USB devices while the computer is running, you still need to exercise caution and make sure you never connect or disconnect a USB device while data transfer is in progress. This can result in damage or at least corrupted data.
USB keyboards and mice
Keep in mind that since USB devices normally won’t work in DOS, you won’t be able to use your USB keyboard or mouse when booting into a pure DOS environment unless your PC has a motherboard that offers USB support in the BIOS. This means that if you ever have to boot from a startup disk, or enter the BIOS to make changes, or use DOS versions of programs like Drive Image or Partition Magic, you can’t use a USB keyboard or mouse. For these situations you might want to check your motherboard/BIOS documentation to find out whether it offers USB support in the BIOS. If not, you should keep a spare non-USB keyboard and/or mouse handy.
You can buy extension cables for USB if you need to connect a printer or scanner that sits across the room. However, don’t forget that signal quality degrades the longer the cable is. For that reason, there are limitations on cable length for USB devices, just as there are for network cables, printer cables, etc. The maximum safe cable length for a USB device is about 15 feet or 5 meters. If you need to cover a longer distance, you should consider using a powered USB hub or repeater to keep the signal from degrading or being corrupted.