A hard disk drive is a mass storage device which is physically similar to a vinyl disk in some key aspects You have a disk the disk has tracks and then you have an arm that has a head with a pin over the extreme that will hang over the disk. At the other end of that arm there a support that in an automatic turntable will move the arm to place the head on any desired track by using a step motor. Well. That it for the close analogy now let go for the HDD Disk and head are also there but in an HDD the support with the step motor is called actuator (nowadays step motors are not used it just magnets) and the arm is called actuator arm. You also have tracks but instead of music in analogue format you have data stored digitally on the magnetic surface of each disk plate. Then the differences start. Here a beautiful cut of an HDD as you see there more than 1 disk (it not always the case there are HDDs with just 1 disk). For each disk there a head hanging from an actuator arm and all connected to the same actuator (multiple heads multiple arms always one actuator = the heads and arms will move in sync). The track is the same concept as in a vinyl disk but this time you are not playing a track but you rather need to read a chunk of it at a time. The minimum chunk that will be accessed and read by the HDD head is called a sector. Then you see there a wire connected to the actutator which leads to somewhere else. Well that how the actuator is connected to the hard disk controller. This is a circuit board with processors and some RAM memory that will decide based on the data request what is going to be retrieved. There a lot more to it and there are great articles around with lots of pictures and explanations on every single aspect (a lot more information than I could ever tell you) but hope this is enough as a starting point for you.