Under Linux, we create filesystems by using a special command called "mkfs", specifying a particular block device as a command-line argument.

However, although it is theoretically possible to use a "whole disk" block device (one that represents the entire disk) like /dev/hda or /dev/sda to house a single filesystem, this is almost never done in practice. Instead, full disk block devices are split up into smaller, more manageable block devices called "partitions". Partitions are created using a tool called fdisk, which is used to create and edit the partition table that's stored on each disk. The partition table defines exactly how to split up the full disk.