Secondary storage is non-volatile storage that holds data and programs permanently — data is retained when the power is switched off. Unlike primary storage (RAM/ROM), the CPU cannot access secondary storage directly; data must be loaded into RAM first.
OCR J277 requires knowledge of three types of secondary storage: magnetic, optical, and solid-state.
1. Magnetic Storage
Magnetic storage uses spinning magnetic platters and a read/write head that moves across the surface to store and retrieve data. Data is stored as magnetic patterns (polarisation) on the platter surface.
Hard Disk Drive (HDD)
Capacity: Very large (500 GB – 20+ TB)
Speed: Moderate (read/write head must physically move)
Cost per GB: Low — cheapest storage per gigabyte
Durability: Fragile — moving parts can be damaged by knocks/drops
Noise: Produces noise from spinning platters
Use cases: Desktop PCs, data centres, network-attached storage
2. Optical Storage
Optical storage uses a laser to read/write data on a reflective disc. Data is stored as pits and lands on the disc surface — a laser reads differences in reflected light.
Use cases: Film distribution, software distribution, archiving
3. Solid-State Storage (Flash Memory)
Solid-state storage uses flash memory — no moving parts. Data is stored electrically in NAND flash memory chips. Examples include SSDs, USB flash drives, SD cards, and mobile phone storage.
SSD (Solid-State Drive)
Capacity: Large (128 GB – 8+ TB)
Speed: Very fast — significantly faster than HDD
Cost per GB: Higher than HDD, falling rapidly
Durability: Very durable — no moving parts
Noise: Silent
Power use: Lower than HDD
Use cases: Laptops, high-performance PCs, mobile devices
Comparison Table
Feature
Magnetic (HDD)
Optical (DVD)
Solid-State (SSD)
Capacity
Very large (TB)
Low-moderate (GB)
Large (GB–TB)
Speed
Moderate
Slow
Very fast
Cost per GB
Lowest
Higher
Higher (falling)
Durability
Fragile (moving parts)
Can scratch
Very durable
Moving parts
Yes (platters, head)
Yes (spinning disc)
No
Power use
Higher
Higher
Lower
Noise
Yes
Yes
Silent
Portable?
Bulky
Yes
Yes (USB/SSD)
Choosing Suitable Secondary Storage
When a question asks you to "justify a choice of storage", always link the storage type to the specific needs:
Large capacity on a budget → HDD (cheapest per GB)
Speed and portability → SSD (fast, no moving parts, laptop-friendly)
Distributing software/films commercially → Optical (cheap to mass-produce)
Portable backup/transfer → USB flash drive (solid-state, very portable)
Exam tip: For "compare" questions, always use comparative language: "SSDs are faster than HDDs" not just "SSDs are fast." For "justify" questions, link the feature (speed/capacity/cost) to the specific scenario given.
⚠️ Common Mistakes
Saying SSDs use optical storage — SSDs use flash memory (electrical), not optical (laser)
Saying optical storage is faster than HDDs — optical drives are generally slower
Forgetting that magnetic storage has moving parts and is therefore more fragile
Saying secondary storage is directly accessible by the CPU — data must be loaded into RAM first
Confusing capacity and speed — HDDs have the most capacity per pound but SSDs are faster
✅ Notes completed!
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Video coming soon
Key points covered in this video
✦Magnetic storage: how HDDs work, platters, read/write head
✦Optical storage: laser, pits and lands, CD/DVD/Blu-ray
✦Solid-state: flash memory, no moving parts, SSDs and USB drives
✦Comparing storage types and justifying choices for different scenarios
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Worksheet — 1.2.2 Secondary Storage
8 questions · 19 marks · Submit to reveal mark schemes
Q1State three types of secondary storage.[3]
✅ Mark scheme
Magnetic (e.g. HDD) [1]; Optical (e.g. CD, DVD, Blu-ray) [1]; Solid-state/flash memory (e.g. SSD, USB flash drive) [1].
Q2Describe how data is stored on a hard disk drive (HDD).[2]
✅ Mark scheme
Data is stored as magnetic patterns on spinning platters [1]; a read/write head moves across the surface to read or write magnetic polarisations [1].
Q3Describe how data is read from an optical disc.[2]
✅ Mark scheme
A laser is shone on the disc surface [1]; pits and lands reflect light differently; the differences in reflected light are interpreted as binary data [1].
Q4Give two advantages of an SSD over an HDD.[2]
✅ Mark scheme
Any two: Faster read/write speeds [1]; No moving parts so more durable/less likely to fail from physical shock [1]; Silent operation [1]; Lower power consumption [1]; Lighter/smaller [1].
Q5A film studio wants to distribute a new movie to customers on physical media. Justify the most suitable type of secondary storage.[3]
✅ Mark scheme
Blu-ray / DVD [1]; Optical media is cheap to mass-produce in large quantities [1]; Blu-ray can hold up to 50 GB which is sufficient for HD film data [1]; Read-only (ROM) format prevents unauthorised copying [1] (any 3).
Q6Give one disadvantage of magnetic hard disk drives compared to SSDs.[1]
✅ Mark scheme
Any one: Slower access/read-write speeds [1]; Has moving parts so more fragile/can fail if dropped [1]; Produces noise [1]; Uses more power [1].
Q7Why is secondary storage described as 'non-volatile'? What does this mean for a user?[2]
✅ Mark scheme
Non-volatile means data is retained when power is removed [1]; this means users' files, programs and the operating system remain stored even when the computer is switched off [1].
Q8Compare the capacity, speed, and cost per GB of HDD and SSD secondary storage.[4]
✅ Mark scheme
Capacity: Both available in TB, HDDs tend to be available in larger capacities per unit [1]; Speed: SSDs are significantly faster than HDDs at read/write [1]; Cost: HDDs are cheaper per GB than SSDs [1]; Overall: SSDs offer speed/durability benefits while HDDs offer lower cost for large capacity storage [1].
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Mini Test — 1.2.2 Secondary Storage
10 questions · 10 marks · 10 minutes
• 5 multiple choice + 5 short answer
• Mark schemes revealed after submission
⏱ 10:00
10 marks
Section A — Multiple Choice [5 marks]
Q1Which type of secondary storage uses a laser to read data?
Q2Which secondary storage type has no moving parts?
Q3Which storage type is cheapest per GB for large capacities?
Q4How is data stored on an HDD?
Q5A student needs fast, portable storage for a laptop. Which is most suitable?
Section B — Short Answer [5 marks]
Q6State what 'pits and lands' are in optical storage.
Mark schemePits are indentations and lands are flat areas on the surface of an optical disc; they reflect laser light differently and are read as binary data (0s and 1s). [1]
Q7State one advantage of HDD over SSD.
Mark schemeHDDs are cheaper per GB / available in larger capacities for lower cost. [1]
Q8Why are SSDs more durable than HDDs?
Mark schemeSSDs have no moving parts so they are not damaged by knocks, drops or vibration; HDDs have spinning platters and a moving read/write head that can be damaged. [1]
Q9State what type of memory is used in solid-state storage.
Mark schemeFlash memory (NAND flash). [1]
Q10Name one example of optical storage and state its approximate capacity.
Mark schemeCD (~700 MB) [1] / DVD (~4.7 GB single layer) [1] / Blu-ray (~25 GB single layer) [1]. [Any correct pairing]