HDD definition

A HDD (Hard Disk Drive, or Hard Drive) is an electronic and mechanical device that stores data magnetically on rigid (hard) spinning disks, called platters. It is a medium of non-volatile and cheap data storage which means it's a popular choice for computers to store large quantities of data for the long term.

Compared to floppy disks, CD's and DVD's, hard disks are permanently sealed in the drive but offer higher speeds, reliability and capacity. Compared to Solid State Drives (which use stationary microchips), HDD's are slower for reading and writing to, especially when the data is fragmented (scattered) across the platters, are less energy-efficient, heavier, noisier, offer lower bit/byte density (thus cannot be smaller and have as much capacity) and are usually less reliable, but are cheaper for their capacity and may have more write-endurance. Thus, they're best for cheap storage solutions and for Digital Video Recorders, where speed and such is not as important, but are much less popular in laptops and tablets or in servers that employ read intensive operations or stores many small files or records.