The world of hard drives and Data Recovery can be full of jargon. Some explanations of the most common terms can be found below.
The PCB, Card or Logic Board is where the electronics and some firmware are stored. The PCB is also where the Power and Data connectors are attached.
The metal or glass disks inside a hard drive, which contain data in magnetic form.
Partly on the PCB and partly on the hard disk surface, firmware is the brain of the hard drive. It makes the motor spin, the heads read/write, and makes logs of errors. Without firmware, a hard drive is just an expensive paperweight.