No one really expects your system to remain stagnant. As your company grows, your computer should be able to grow with it. You can add more memory or a new printer with little or no changes to the operating system itself. However, if you need to add something like a hard disk or CD-ROM drive, you may need to tell the operating system about these changes, especially if the piece you are adding is the first of its kind.

You tell Linux that you have new hardware by linking in the appropriate drivers in the kernel. This is done when you run the make conf when you are asked a series of questions about your hardware. In newer distributions, you will find in your kernel source directory a subdirectory, Documentation, that contains some very detailed information about what to look out for.

As when you add any device to your system, I need to remind you to have everything planned out before you start. Know what hardware exists on your machine and what settings each card has. Look at the documentation to see what settings are possible in case you need to change them. If you are adding a new device of a particular type, the odds are that you are going to need to make some changes.

In ancient times (relatively speaking), you had to shutdown your computer, unplug the power, then ground yourself before even thinking about opening up the case in order to prevent a elctrostatic discharge and destroying the sensative components. Today, computer components are less sensative (although these are still good ideas) and many devices can be removed and added without having to even shutdown the operating system, let alone turn off the machine. This is called “hot swapping” in that a device is “swapped” (i.e. replaced) while the system is hot (i.e running). In constast to this is “cold swapping“, where the device can only replaced when the machine is turned off. Note that this is also referred to as “hot plugging” or “cold plugging”

At first, hotswapping in computers was limited to hard disks, but currently many othe devices, even entire expansion boards and even RAM, can be hot swapped. Typically special connects are used to ensure that specific pins make contact before others, for example my making some pins shorter, or even various lengths depending on the function of the pin. One common feature is that the ground pin is longer, so that the devices are ground before any other connection is made. Often the connector itself is designed to ensure that specific pins connect before others.

One very common form of hot plugging is USB. When hotplugable devices are added to the system, they are normally recognized and the system runs the hotplug, which notifies user mode software the device has been added.

It is extremely important to keep in mind that hot swapping needs to be supported by both the machine and the operating system. Ensure you know beforehand! It can cause serious problems if you think a machine supports hot swapping when it doesn’t, even to the point of damaging other components. Also keep in mind that depending on the type of device you may need to first tell the operating system that the device is no longer accessible or tell the operating system to stop using the device. For example, while nothing prevents you fom simply pulling the plug on an external USB devic, you can potentially lose data if you don’t first unmount the filesystem.