In short: an HDD (Hard Disk Drive) is a device for long-term data storage on spinning magnetic platters. It holds your files, programs, photos and videos, and they stay there after the computer is switched off. Today people choose an HDD when they need lots of space for little money.
What HDD stands for
HDD stands for Hard Disk Drive. "Hard" as opposed to floppy disks, whose storage medium was a flexible film. HDD platters are rigid: they are made of glass or aluminium alloy with a magnetic coating.
Other names for a hard drive
- Hard disk, hard drive - the everyday names.
- Winchester - an old nickname from the 1970s. One IBM model had the internal designation "30-30", like the famous Winchester rifle, and the name stuck. It is still common in Ukraine and Eastern Europe.
- Storage drive - a broader term covering HDDs, SSDs and flash drives.
- HDD - the most precise technical name.
In everyday speech these all mean the same thing. An SSD, however, is a different device, even though people sometimes call it a "disk" too.
How a hard drive is built
- Platters with a magnetic coating that store the data. A drive can have anywhere from one to ten or more.
- Spindle - the motor that spins the platters at 5400 or 7200 rpm.
- Read/write heads float nanometers above the platter surface without touching it.
- Actuator - the mechanism that moves the heads to the right track.
- Controller and cache - the circuit board that runs the drive and exchanges data with the computer.
Because of these mechanics, an HDD is slower than an SSD with small files and sensitive to shocks while running. Why spindle speed affects performance is explained in 5400 vs 7200 rpm.
Why HDDs when SSDs exist
- Price per terabyte. An HDD is several times cheaper for the same capacity.
- Large capacities. 8, 12, 16 TB and larger hard drives are standard products, while SSDs of that size cost many times more.
- CCTV and NAS. 24/7 recording quickly wears out an SSD, while dedicated HDDs are designed for it.
- Archives and backups. An external HDD is the most affordable way to keep a copy of important data.
A comparison of the two drive types is in HDD vs SSD.
Types of hard drives
- 3.5" - for desktop PCs, NAS and recorders: drives for PC.
- 2.5" - for laptops and external enclosures: laptop drives.
- External - a drive in a USB enclosure that connects without opening the computer: external HDDs.
- Dedicated series - for CCTV, for NAS, server.
A brief history
The first production hard drive, the IBM 350, appeared in 1956 as part of the IBM RAMAC computer. It was the size of a wardrobe, had fifty 24-inch platters and held about 5 million characters. A modern palm-sized 3.5" drive stores millions of times more.
