A server these days can be anything from a home unit serving MP3's and homework
files to the kids, to a machine running a business-critical system for a small
business, to a 3u rack mount unit serving up millions of hits a day on the internet.
The thing that most servers have in common is that they are always on and
therefore reliability is a key characteristic. Also they serve more than one user
while storing and processing important information. For this reason servers are
often equipped with redundant systems such as dual power supplies, RAID 5
arrays of four or more hard disks, special server grade processors that require
error-correcting memory, multiple high-speed Ethernet connections, etc.
All of this is a little beyond the scope of the current work, but, in general,
servers need lots of RAM, fast redundant hard drives, and the most reliable
components your budget will allow. On the other hand, since nobody is usually
sitting at them, you can get away with the cheapest possible keyboard,
mouse and monitor (in fact many servers run “headless” with no monitor at
all). Graphics are also a very low priority on these machines, and a read only
CD/DVD-ROM optical drive (used, infrequently, for installing software and
updates) will do just fine.