Learning Objectives
By the end of this chapter, you will be able to:
- Define secondary storage and its purpose.
- Describe how a Hard Disk Drive (HDD) works.
- Describe how a Solid-State Drive (SSD) works and its advantages over an HDD.
- Identify common types of optical storage.
- Describe portable, network, and cloud storage.
- Choose a suitable storage and backup solution for a business.
Secondary Storage Devices
Secondary storage refers to the non-volatile devices and media used for long-term storage of data and programs. Unlike primary memory (RAM), secondary storage retains its data even when the computer is turned off.
Storage units
| Unit | Size | Roughly holds |
|---|---|---|
| Kilobyte (KB) | 1,024 bytes | A short text document |
| Megabyte (MB) | 1,024 KB | A high-quality photo (3–5 MB) |
| Gigabyte (GB) | 1,024 MB | About an hour of HD video |
| Terabyte (TB) | 1,024 GB | Hundreds of thousands of photos |
Storage manufacturers usually count 1 GB as 1,000 MB, which is why a “1 TB” drive shows about 931 GB in Windows.
1. Hard Disk Drives (HDD)
For decades, the Hard Disk Drive was the primary form of secondary storage in computers.
- How it Works: An HDD is a mechanical device that stores data on rapidly rotating platters with magnetic surfaces. A read/write head on a mechanical arm moves across the platters to read and write data.
- Characteristics: HDDs offer very large storage capacities at a low cost per gigabyte. However, because they have moving parts, they are slower, less durable, and consume more power than newer technologies.
- Speed is partly set by rotation speed, typically 5,400 or 7,200 RPM. Dropping a running HDD can damage the platters and lose data.
2. Solid-State Drives (SSD)
Solid-State Drives are now the standard for primary storage in modern laptops and desktops.
- How it Works: An SSD has no moving parts. It stores data on interconnected flash-memory chips.
- Characteristics: Because they have no moving parts, SSDs are significantly faster, more durable, quieter, and more power-efficient than HDDs. However, they are more expensive per gigabyte.
- Types: SATA SSDs use the same connection as HDDs; NVMe SSDs plug into an M.2 slot and are several times faster.
3. Optical Storage
Optical storage devices use a laser to read and write data on a spinning disc.
- How it Works: A laser beam creates tiny pits in the surface of the disc to represent data. Another laser reads these pits.
- Characteristics: Optical discs are portable and inexpensive, but they have a much smaller capacity and are much slower than HDDs and SSDs. They are becoming less common in modern computers.
- Examples: Compact Discs (CDs), Digital Versatile Discs (DVDs), and Blu-ray Discs.
| Disc | Typical capacity |
|---|---|
| CD | About 700 MB |
| DVD | 4.7 GB (single layer) |
| Blu-ray | 25 GB (single layer) |
4. Flash and Portable Storage
- USB flash drives (pen drives) and memory cards (SD, microSD) use flash memory; they are small, cheap, and portable, but easy to lose and can spread malware.
- External HDDs and SSDs connect by USB and are commonly used for backups.
5. Network and Cloud Storage
- NAS (Network Attached Storage): a storage device on the office network that everyone can share and back up to.
- Cloud storage: files stored on a provider’s servers over the internet, such as Google Drive, OneDrive, and Dropbox. Accessible anywhere and protected from local disasters, but needs internet and raises privacy questions.
6. Magnetic Tape
Still used by banks and data centers for archival backups, because tape is very cheap per terabyte and durable, though slow to access (sequential access).
Comparison
| Feature | HDD | SSD | Optical disc | USB flash drive | Cloud storage |
|---|---|---|---|---|---|
| Technology | Magnetic, moving parts | Flash memory, no moving parts | Laser | Flash memory | Provider’s servers |
| Speed | Moderate | Very fast | Slow | Moderate | Depends on internet |
| Capacity | Very large (TBs) | Large | Small | Small to moderate | Scalable |
| Cost per GB | Low | Higher | Low | Moderate | Subscription |
| Durability | Sensitive to shocks | Shock resistant | Scratches easily | Easy to lose | Safe from local damage |
| Typical use | Bulk storage, backups | OS and apps, laptops | Distribution, archives | Transfer files | Sharing, backup, remote access |
Backup: The 3-2-1 Rule
Storage devices fail, get stolen, or are hit by ransomware. A simple backup rule for businesses is 3-2-1:
- Keep 3 copies of important data,
- on 2 different types of storage (e.g., office PC and external drive),
- with 1 copy off-site (e.g., cloud storage or a drive kept at another location).
Scenario: a small clinic in Dharan keeps patient records on its reception PC (copy 1), backs them up nightly to a NAS (copy 2), and syncs encrypted backups to cloud storage (copy 3, off-site). When the reception PC’s drive fails, records are restored within an hour.
Summary
Secondary storage devices provide the long-term, non-volatile memory for a computer. The main types are mechanical Hard Disk Drives (HDDs), which offer large capacity at a low cost, and Solid-State Drives (SSDs), which have no moving parts and are much faster and more durable. While once common, optical drives like CD/DVD drives are now largely being replaced by faster and more convenient storage solutions such as flash drives, NAS, and cloud storage, while magnetic tape remains in use for archives. Businesses should combine these in a backup plan such as the 3-2-1 rule.
Key Takeaways
- Secondary storage is non-volatile and used for long-term data storage.
- HDDs are mechanical drives with high capacity and low cost.
- SSDs are flash-based drives that are much faster and more durable than HDDs.
- Optical drives (CD, DVD, Blu-ray) are a slower, portable storage format.
- Flash drives, NAS, cloud, and tape serve portability, sharing, and archiving.
- The 3-2-1 backup rule protects business data.
Discussion Questions
- What are the main advantages of an SSD over an HDD?
- If you were buying a new computer today, would you choose one with an HDD or an SSD? Why?
- Why are optical drives becoming less common in modern computers?
Exam-Style Questions
Short answer
- What is secondary storage? Give four examples.
- Differentiate between HDD and SSD.
- What is cloud storage? State one advantage and one disadvantage.
Long answer
- Explain the different types of secondary storage devices and compare them.
- Suggest a storage and backup plan for a small business, explaining the 3-2-1 rule.
