Secondary storage is a core topic in IB Computer Science because it explains how data is stored permanently. Unlike RAM, secondary storage is non-volatile, meaning data is retained even when power is switched off.
IB students are expected to understand the main types of secondary storage devices, how they work, and when each is used. The most important devices to compare are Hard Disk Drives (HDDs), Solid State Drives (SSDs), and Network Attached Storage (NAS).
What Is Secondary Storage?
Secondary storage is used to:
- Store operating systems
- Store software and applications
- Store user files and data
- Retain data long-term
It is slower than RAM but much larger in capacity and non-volatile.
Hard Disk Drives (HDDs)
HDDs store data using magnetic platters that spin at high speed.
Key characteristics:
- Mechanical components
- Large storage capacity
- Lower cost per gigabyte
- Slower access times compared to SSDs
Data is read and written using a moving read/write head, which causes delays due to physical movement.
In IB answers, HDDs are often associated with:
- Desktop computers
- Servers requiring large storage
- Backup systems
Their main disadvantage is slower performance and higher risk of mechanical failure.
Solid State Drives (SSDs)
SSDs store data using flash memory, with no moving parts.
Key characteristics:
- Very fast read/write speeds
- No mechanical components
- More durable and reliable
- More expensive per gigabyte than HDDs
Because SSDs have no moving parts, data access is almost instantaneous compared to HDDs.
In IB Computer Science, SSDs are commonly linked to:
- Faster boot times
- Improved system performance
- Laptops and modern computers
SSDs are especially important in performance-based comparisons.
Network Attached Storage (NAS)
NAS is a storage system connected to a network, rather than directly to a single computer.
Key characteristics:
- Centralised storage
- Accessible by multiple devices
- Often used in homes, schools, and businesses
- Can use HDDs or SSDs internally
NAS allows users to:
- Share files across a network
- Perform automatic backups
- Access data remotely
In IB exams, NAS is often linked to data sharing and network storage, not raw speed.
Comparing HDDs, SSDs, and NAS
For IB Computer Science, students should compare devices based on:
- Speed: SSDs fastest, HDDs slower
- Cost: HDDs cheapest per gigabyte
- Reliability: SSDs more durable
- Accessibility: NAS supports multiple users
Each device serves a different purpose.
Common Student Mistakes
Students often:
- Say SSDs permanently replace HDDs
- Confuse NAS with cloud storage
- Ignore cost and capacity trade-offs
- Focus only on speed
Balanced comparisons score higher.
Final Thoughts
HDDs, SSDs, and NAS are all essential secondary storage solutions, each designed for different needs. HDDs prioritise capacity and cost, SSDs prioritise speed and reliability, and NAS prioritises shared network access.
Understanding these trade-offs allows IB Computer Science students to explain storage decisions clearly and accurately — exactly what examiners expect.
