How do disks work, on UNIX mostly, as well as in general?

A disk sector (or block) is 512 contiguous bytes, as well as a header and trailer with error checking information, on one side of a disk platter under one head.

A track is the entire length of the path that a disk head traces over one side of a disk platter. A track is made up of multiple sectors.

A cylinder is the collection of tracks on multiple platters on a single position of the heads.

On Solaris, disk slices are groups of cylinders which are used by a file system.

On Solaris, disk slices have two flags - w or r (writable vs. read-only) and m or u (mountable, like a normal file system, or unmountable like swap or backup).