You can determine whether hardware is Linux® compatible by visiting the official website of the specific distribution, or flavor, that you intend to run. There typically is a link to a list of compatible hardware. If you have the installation compact discs (CDs) or the digital versatile disc (DVD), you might be able to consult the release notes on them, which can give very valuable information about compatibility. Release notes are stored in a file on the disc. Other ways to determine whether hardware is Linux® compatible include consulting the official website of the manufacturer of the device or the site of the manufacturer of the particular personal computer (PC) model or laptop that you have.
One of the first steps to take in determining whether hardware is Linux® compatible is learning that almost all distributions run on similar platforms. It is also helpful to keep in mind that generally controller-less modems, also known as "win" or "soft" modems, tend to be very problematic, and most are not Linux® compatible at all. If you plan to have a dial-up connection to the Internet, it is highly advisable to obtain a controller-based modem, also called a hardware modem, in order to avoid compatibility problems.
There are a good number of frequently updated web sites that specialize in helping you to determine if a piece of hardware is Linux® compatible. Some are dedicated to a particular type of hardware, such as printers. Performing an Internet search using the keywords "Linux printing" or "modems for Linux" will display ample options linking to the information you need. You should read the information carefully, because detailed sites will specify when a piece of hardware is only partially Linux® compatible. This information is usually based on user feedback, which tends to be quite reliable.
Reading the system requirements printed on the package of hardware will sometimes reveal whether the device is Linux® compatible. Such helpful information rarely appears on the packaging of hardware, but it is worth at least taking a look for it. Most devices such as digital cameras don't require the installation of software in order to function. This almost always means that the hardware is Linux® compatible, because it tends to mount as a file system when plugged into a universal serial bus (USB) port. Although economical printers tend to be problematic, printers — particularly those that are commercial grade network printers — are almost always compatible.
Many veteran users actually prefer to research Linux® compatibility by visiting the community forums for the particular distribution they run. Members of these forums can provide you with an excellent unofficial answer that is often just as accurate, if not more accurate, than an official one, because they represent how the distribution and device behave on a variety of platforms and under various configurations. There is often someone in the forum who can provide you with free technical support that solves compatibility issues.