Hard disk drive
The Hard disk drive, also known as HDD, hard drive, hard disk and disk drive, is the main secondary (permanent) storage device used in computers, including laptops. The hard disk drive stores, among other things, the operating system, installed programs and user's files.
Laptops manufactured before the year 2003 use IDE (Integrated Device Electronics) (also called PATA, short for Parallel ATA) hard disk drives, whereas newer laptops use SATA (Serial ATA) hard disk drives.
Hard disk drives' storage capability is measured usually in gigabytes (GB). The size of hard disk drives has dramatically increased within the last 10 years or so. 
- Solid-state drive (SSD)