Everything is consider a file in Linux, so your hard disk is kept track of as a file that sits there.
If you’re using an SATA hard drive as example, your hard drive will be known as /dev/sda. there is /dev/cdrom ,/dev/cdwriter , /dev/hda “IDE hard drive”.
Not only physical devices also all data are stored as files. in short
“IN LINUX, EVERYTHING IS A FILE“