What is Storage?
Unlike RAM, which loses data when the power goes off, storage devices keep your files, programs, and the operating system permanently. Every photo, video, game, and document on your computer lives on a storage device until you delete it.
Storage devices are sometimes called secondary storage because the CPU cannot directly use them — data must first be loaded into RAM (primary storage) before it can be processed.
Hard Disk Drives (HDDs)
A Hard Disk Drive (HDD) is a traditional mechanical storage device. Inside, it has spinning magnetic discs (platters) and a moving read/write head that stores and retrieves data magnetically.
- Capacity: Very high — 1 TB to 20 TB is common
- Speed: Slower than SSDs due to mechanical movement
- Cost: Cheap per gigabyte
- Durability: Fragile — the moving parts can break if dropped
HDDs store data on spinning magnetic platters. The faster the platters spin (measured in RPM — revolutions per minute), the quicker the drive can read and write data. Common speeds are 5,400 RPM and 7,200 RPM.
Solid State Drives (SSDs)
An SSD (Solid State Drive) stores data on flash memory chips — the same technology used in USB drives and memory cards. There are no moving parts.
- Speed: Much faster than HDDs (boot times are seconds instead of minutes)
- Durability: More reliable — no moving parts to break
- Cost: More expensive per gigabyte than HDDs
- Capacity: 256 GB to 4 TB for consumer models
Comparison Table
| Feature | HDD | SSD |
|---|---|---|
| Speed | Slower | Much faster |
| Durability | Fragile (moving parts) | More durable |
| Cost per GB | Cheap | More expensive |
| Capacity | Up to 20 TB | Up to 4 TB |
| Noise | Makes noise | Silent |
| Best for | Large file storage | System drive / boot |
Other Storage Devices
- USB Flash Drives: Portable, solid-state. Great for transferring files between computers.
- Optical Discs (CD, DVD, Blu-ray): Use a laser to read and write data. Being replaced by downloads and streaming.
- Memory Cards (SD cards): Used in cameras, smartphones, and handheld consoles.
- Cloud Storage: Data stored on remote servers accessed over the internet (Google Drive, iCloud, OneDrive).
Many modern computers use an SSD as the main drive (for speed) alongside a large HDD (for cheap bulk storage). This gives the best of both worlds.
Practice Problems
Give two advantages of an SSD over an HDD for use as a laptop's main storage drive.
Show answer
A student wants to back up their entire photo library (200 GB) cheaply and does not need fast access to the backup. Which type of storage device would you recommend and why?