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OCR J277 · Component 1 · Topic 1.2.2
Secondary
Storage
Optical · Magnetic · Solid State
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OCR GCSE Computer Science J277
Learning Objectives
By the end of this video you will be able to...
Explain why computers need secondary storage
Describe the characteristics of optical, magnetic and solid state storage with examples of each
Compare storage types using the six characteristics: capacity, speed, portability, durability, reliability, cost
Choose a suitable storage device for a given scenario and justify your answer
⚡ The exam always gives you a scenario — you must choose a storage type AND justify using the six characteristics
Why is Secondary Storage needed?
Secondary storage stores data long-term
THE CORE REASON
Secondary storage is needed to store data and files long-term / permanently. RAM is volatile — it loses data when power is off. Secondary storage retains data without power.
Stores the user's files, documents, photos, videos, programs, and the operating system permanently
Stores data that is not currently being used — only active data moves into RAM
Also used by virtual memory — when RAM is full, data is transferred to secondary storage temporarily
Three Types of Secondary Storage
Optical · Magnetic · Solid State
💿
Optical
CD · DVD · Blu-ray
🖥️
Magnetic
HDD (Hard Disk Drive)
💾
Solid State
SSD · USB flash drive · SD card
The six characteristics used to compare them: capacity · speed · portability · durability · reliability · cost
⚠ Not required: how each type works internally (component parts). Focus on the characteristics and when to use each type.
Optical Storage
CD · DVD · Blu-ray
ADVANTAGES
Portable — discs are lightweight and easy to carry and share
Cheap to produce — low cost per disc, especially for distributing content
Widely compatible — most computers and devices can read them
Long shelf life if stored correctly
DISADVANTAGES
Low capacity — CD ~700 MB, DVD ~4.7 GB, Blu-ray ~25 GB — much less than HDD or SSD
Slow read/write speed compared to magnetic and solid state
Fragile — discs can be scratched, reducing reliability
Many modern devices no longer include a disc drive
📝 Best for: distributing software, music, films; archiving; sharing data cheaply
Magnetic Storage
HDD — Hard Disk Drive
ADVANTAGES
High capacity — HDDs commonly hold terabytes of data
Low cost per GB — cheaper per unit of data than solid state
Widely available and well-established technology
Sufficient speed for general use — adequate for desktop computers
DISADVANTAGES
Has moving parts — can be damaged if dropped or moved during use
Slower than solid state — mechanical movement limits access speed
Heavier and larger — less portable than SSD or USB
Files can become fragmented — needs defragmentation over time
📝 Best for: desktop computers, servers, large file storage where portability is not needed and cost matters
Solid State Storage
SSD · USB Flash Drive · SD Card
ADVANTAGES
No moving parts — very durable and resistant to physical shock
Faster access speed than magnetic — programs load more quickly
Portable (especially USB/SD) — small, lightweight, easy to carry
Silent, low power consumption — suitable for laptops
No fragmentation — consistent access time
DISADVANTAGES
Higher cost per GB than magnetic storage
Lower capacity than HDD at the same price point
Data can be lost if the device is damaged or corrupted
📝 Best for: laptops, portable devices, situations where speed, durability, or portability matters more than cost
Comparison — Six Characteristics
How the three types compare
| Characteristic |
💿 Optical |
🖥️ Magnetic |
💾 Solid State |
| Capacity | Low (MB–GB) | High (TB) | Medium–High (GB–TB) |
| Speed | Slow | Medium | Fast |
| Portability | High (discs) | Low (heavy) | High (USB/SD) |
| Durability | Low (scratches) | Medium (moving parts) | High (no moving parts) |
| Reliability | Lower (can scratch) | Medium | High |
| Cost | Low per disc | Low per GB | Higher per GB |
Applying Knowledge — Scenarios
Choosing the right storage for the context
SCENARIO 1 — MUSICIAN'S DESKTOP COMPUTER
Large sound files, computer stays on desk, cost matters, does not need to move → Magnetic (HDD): high capacity, low cost per GB, does not need to be portable, computer is unlikely to move so moving parts are not a risk
SCENARIO 2 — LAPTOP / PORTABLE DEVICE
Device is carried around, speed matters, battery life matters → Solid State (SSD): no moving parts so durable when moved, faster access speed, lower power consumption
SCENARIO 3 — DISTRIBUTING SOFTWARE / SHARING FILES CHEAPLY
Small files, needs to be cheap to produce and share widely → Optical (DVD/CD): low cost per disc, portable, widely compatible — though capacity is limited
Exam Practice
Pause and have a go before the answer appears
Question 1
State two reasons why a computer needs secondary storage.
2 marks
✓ MARK SCHEME
1 mark
To store data / files long-term / permanently — data is retained when the power is off
1 mark
To store data / programs that are not currently being used / not currently in RAM
Either mark: RAM is volatile so secondary storage is needed to retain data when power is off — this links both points
Exam Practice
Question 2
Identify the type of secondary storage (optical, magnetic, or solid state) for each device:
Hard Disk Drive (HDD) — USB Flash Drive — DVD — SSD
4 marks
✓ MARK SCHEME
1 mark
USB Flash Drive → Solid State
Exam Practice
Question 3 — Scenario (2024 style)
A musician uses a desktop computer that stays on their desk. They store large sound files. Justify a suitable type of secondary storage for this computer.
4 marks
✓ MARK SCHEME — Magnetic (HDD)
1 mark
High capacity — file sizes of sound files can be large, so a high capacity drive is needed
1 mark
Low cost per GB — magnetic is cheaper per unit of data than solid state
1 mark
Computer is unlikely to move — so the moving parts of a HDD are not a risk of damage
1 mark
Sufficient speed — no significant delays in storing/reading data for this use case
Each point must be applied to the context — link capacity to "large sound files", moving parts to "stays on desk"
Exam Practice
Question 4
Describe two advantages of solid state storage over magnetic storage.
2 marks
✓ MARK SCHEME
1 mark
No moving parts — solid state is more durable / less likely to be damaged if dropped or moved
1 mark
Faster access speed — programs and files load more quickly than with magnetic storage
Other valid marks: lower power consumption, silent, no fragmentation, more portable (USB/SSD). Each advantage must be stated clearly — "it is better" alone is too vague.
Common Mistakes
Don't lose easy marks
1
Saying a storage type is "better" without applying it to the context. Exam questions give you a scenario — you must link the characteristic to the specific situation. "High capacity, so it can store the large sound files" gets the mark. "High capacity" alone may not.
2
Confusing magnetic and solid state. Magnetic = HDD, has moving parts, cheaper per GB, larger capacity for the price. Solid state = SSD/USB, no moving parts, faster, more durable but more expensive per GB.
3
Saying optical storage is durable. Optical discs are fragile — they can be scratched. Solid state is the most durable because it has no moving parts.
4
Saying "it is cheap" without specifying what is cheap. For magnetic say cheap cost per GB / per unit of data. For optical say cheap per disc. Vague cost answers lose marks.
Topic Summary — 1.2.2
What You Need to Know
OPTICAL
CD, DVD, Blu-ray
✓ Portable, cheap per disc
✗ Low capacity, slow, fragile
Use: distributing/sharing files
MAGNETIC
HDD
✓ High capacity, low cost per GB
✗ Moving parts, slower than SSD
Use: desktop computers, servers
SOLID STATE
SSD, USB, SD card
✓ Fast, durable, portable, silent
✗ Higher cost per GB
Use: laptops, portable devices
6 Characteristics: Capacity · Speed · Portability · Durability · Reliability · Cost — always link your answer to the context in the question
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Next Video
1.2.3
Units of Data
Bits · Bytes · KB · MB · GB · TB · Calculations
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