Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware. The hardware of a computer is infrequently changed, in comparison with software and data, which are "soft" in the sense that they are readily created, modified or erased on the computer. Firmware is a special type of software that rarely, if ever, needs to be changed and so is stored on hardware devices such as read-only memory (ROM) where it is not readily changed (and is therefore "firm" rather than just "soft").
specification of a computer

1. Hard Disk
   
2. Mother Board
3. RAM
4. Processor

the above are the most essential parts for the CPU ( central processing unit ). Each of which can be further categorized depending on the quality and quantity.