Most small businesses with 10 or more employees will face the task of buying a computer server, or adding to their existing inventory. Servers are most commonly used as central file repositories where users can easily share documents, but they can do many other tasks as well--from print and mail serving to performing system-wide backups. Other key applications include hosting databases, running groupware (such as calendar programs and customer relationship management software), and serving a company Web site or intranet. For creative studios or departments, a server might hold large image, video, and music libraries.
The type of server you choose should reflect the number and type of applications you want to run on it, and the number of users (clients) it will have. Many common applications--such as print serving, sharing office documents like Word and Excel files, and running calendar programs--impose such light processing demands that a single low-cost server may be able to handle your entire company with ease. Other tasks, like hosting large databases or image libraries, require more processing horsepower along with big, fast hard disks and capacious network pipes to match.
Servers are basically specialized PCs, and they run the gamut of speeds and capacities just as desktop workstations do. Nevertheless, they are a breed apart, designed to be secure (to protect your valuable company data) and fault-tolerant (to be available continuously). Servers also offer remote-management tools, so that an IT person can log in from a desk or workstation and check usage, diagnose problems, and perform routine maintenance such as adding new users or changing passwords.
After determining the functions you need your server(s) to perform, and the number of users you will have, you'll need to select a server operating system, such as Windows, Linux, or Mac, and choose the hardware to run it on. If you're upgrading existing servers, you'll probably want to stick with the same type, for easier migration. For new servers, you're free to pick the combination of software and hardware that best meets your needs and budget. Don't assume that because you have PCs, you are locked into Windows; both Linux and Mac servers can handle Windows clients with aplomb, and tend to be much cheaper overall.