The Unix philosophy that "everything is a file" is common to Linux (as is every other Unix philosophy). You even access your hardware through a file. For example, you can send a file out through your serial port by just redirecting some text to the file "/dev/ttyS0" (echo "hello serial port" > /dev/ttyS0). All of these special device files are located in a directory called "dev" directly off of the root of your drive. Other examples of device files are "/dev/cdrom" for cdrom drives, "/dev/hda1" for the first partition on your ide disk drive and "/dev/video0" for the first video capture device.

Note: disk drives in linux follow a certain naming convention. IDE drives will be called /dev/{hda,hdb,hdc,hde} for the first and second drive on your primary controller, and your first and second drive on your secondary controller. Partitions on these disks are addressed by appending a number (based at 1) to the drive name. For example, the first partition on the second drive attached to the primary controller would be designated by "/dev/hdb1". SCSI drives are designated in much the same way except the they start with an s instead of an h (eg. /dev/sda2).