📚 Knowledge Library — Topic 3.7B — Hardware

Secondary Storage

Understand how computers keep files permanently using magnetic, optical and solid-state storage.

Start LearningWorked Example
1. Invitation

Some data needs to stay when power is off.

Primary storage helps the CPU work now. Secondary storage keeps data for later.

Secondary storage is non-volatile storage used to keep files, programs and data permanently.

💡 Remember: secondary storage keeps data even when the computer is turned off.
Figure 1.1
Permanent Storage
Power off
↓
Files stay

Power on
↓
Files still there
2. Big Idea

Secondary storage is long-term storage.

Documents, photos, videos, games and applications are usually stored on secondary storage.

The CPU does not normally access secondary storage directly. Data is loaded into RAM when it is needed.

💡 Big idea: secondary storage keeps data permanently; RAM holds data while it is being used.
Figure 2.1
Storage Journey
SSD / HDD
↓ load
RAM
↓ use
CPU
3. FutureLogic Bridge

Think of a filing cabinet.

Your desk holds the work you are using right now. Your filing cabinet stores work you want to keep.

Secondary storage is the filing cabinet. It is larger and permanent, but not as quick as the desk.

💡 Bridge: RAM is the desk. Secondary storage is the filing cabinet.
Figure 3.1
Filing Cabinet Model
Desk
= current work

Cabinet
= saved files
4. Worked Example

Opening a saved file.

When you open a saved document, it starts on secondary storage.

The document is loaded into RAM so the CPU can work with it.

Opening homework.docx

File stored
on SSD
Loaded
into RAM
CPU
processes it
Secondary storage keeps the file. RAM is used while editing it.
Figure 4.1
Saved File
Stored file
↓
Open file
↓
Work in RAM
5. Magnetic Storage

Magnetic storage uses magnetised surfaces.

A hard disk drive, or HDD, uses spinning magnetic platters.

A read/write head changes tiny areas on the surface to represent binary 0s and 1s.

🎯 Exam Tip: an HDD is magnetic storage. It is not optical storage.
Figure 5.1
HDD
Spinning platter
+
Read/write head
↓
Magnetic 0s and 1s
6. Optical Storage

Optical storage uses lasers.

CDs, DVDs and Blu-ray discs are examples of optical storage.

A laser reads patterns of pits and lands on the disc. When writing, a laser can create pits on the surface.

💡 Optical storage uses light. Magnetic storage uses magnetism.
Figure 6.1
Optical Disc
Laser
↓
Pits + lands
↓
Binary values
7. Solid-State Storage

Solid-state storage has no moving parts.

SSDs, USB flash memory drives and SD cards are solid-state storage.

They use electronic circuits and transistors to store data. Because there are no moving parts, they are fast, quiet and more durable.

🎯 Exam Tip: write USB flash memory drive, not just USB.
Figure 7.1
Solid-State
Tiny switch grid
↓
Charges stored
↓
No moving parts
8. Exam Tip

Compare both sides.

When comparing storage types, give both sides of the difference.

For example, do not just write that SSD is faster. Say that SSD is faster than optical storage because it has no moving parts.

TypeKey idea
MagneticPlatters, read/write head, magnetism
OpticalLaser, pits and lands
Solid-stateTransistors, no moving parts
🎯 Exam Tip: comparisons need both storage types, not just one.
Figure 8.1
Compare Clearly
SSD
= no moving parts

HDD
= moving parts
9. Common Mistake

Do not confuse the storage types.

Students often mix up the technology used by each storage type.

Remember: HDD uses magnetism, optical discs use lasers, and solid-state storage uses electronic circuits.

⚠️ Common Mistake: an HDD has spinning platters, but that does not make it optical. HDD is magnetic.
Figure 9.1
Keep Them Separate
HDD = magnetic
CD/DVD = optical
SSD = solid-state
10. Summary

Secondary storage in one screen.

Secondary storage is non-volatile and keeps data permanently.

Magnetic storage uses magnetised surfaces. Optical storage uses lasers and pits. Solid-state storage uses electronic circuits and has no moving parts.

💡 Key idea: secondary storage keeps files long-term, even when power is off.
Figure 10.1
Three Types
Magnetic
Optical
Solid-state
↓
Permanent storage