Secondary Storage
IB Syllabus: A1.1.7 — Describe secondary storage devices
Table of Contents
- Key Concepts
- Worked Examples
- Quick Code Check
- Spot the Error
- Fill in the Blanks
- Predict the Output
- Practice Exercises
- Connections
Key Concepts
Why Secondary Storage?
Primary memory (RAM) is volatile — it loses all data when the power is turned off. Computers need a way to store programs, files, the operating system, and user data permanently. This is the role of secondary storage.
Four reasons secondary storage is essential:
- Non-volatile — retains data without power
- Larger capacity — typically hundreds of gigabytes to many terabytes, far exceeding RAM
- Cheaper per GB — storing 1 TB in RAM would cost thousands; a 1 TB HDD costs under $50
- Permanent file storage — stores the OS, applications, documents, media, and backups
Internal Storage
SSD (Solid State Drive)
An SSD stores data using NAND flash memory — electronic circuits with no moving parts.
- Very fast read/write speeds (~500 MB/s for SATA; up to 7000 MB/s for NVMe)
- Highly durable — no mechanical components to break from drops or vibration
- Silent operation — no spinning disks or moving heads
- More expensive per GB than HDD
- Common in modern laptops, desktops, and servers where speed matters
- Limited write endurance — each flash cell can only be written a finite number of times (though modern SSDs last many years under normal use)
HDD (Hard Disk Drive)
An HDD stores data on magnetic platters that spin at high speed (typically 5400 or 7200 RPM). A read/write head moves across the platters to access data.
- Slower than SSD (~100-200 MB/s typical)
- Cheapest per GB — ideal for bulk storage
- High capacity available — consumer drives up to 20 TB
- Moving parts make it susceptible to physical damage from drops or vibration
- Produces noise and heat from the spinning motor
- Still widely used in servers, backup systems, and NAS devices
eMMC (Embedded MultiMediaCard)
eMMC is flash storage soldered directly to the motherboard.
- Slower than a full SSD but cheaper to manufacture
- Cannot be upgraded or replaced by the user
- Common in budget laptops, tablets, Chromebooks, and smartphones
- Typical capacities: 32-128 GB
- Suitable for light workloads (web browsing, document editing) but not for high-performance computing
External Storage
External SSD / HDD — portable versions of internal drives connected via USB or Thunderbolt. Used for backup, transferring large files, or expanding storage.
Optical discs — data is read and written using a laser. Three main types:
- CD (Compact Disc): ~700 MB
- DVD (Digital Versatile Disc): ~4.7 GB (single layer)
- Blu-ray: ~25 GB (single layer), ~50 GB (dual layer)
Flash drives (USB sticks) — compact, portable NAND flash storage. Plug into a USB port. Typical capacities range from 8 GB to 256 GB. Very popular for quick file transfers between computers.
Memory cards — SD and microSD cards used in cameras, phones, drones, and handheld devices. Small form factor, moderate speeds, capacities from 8 GB to 1 TB.
NAS (Network Attached Storage) — a dedicated storage device connected to a local network. Contains multiple HDDs or SSDs. Allows multiple users to access shared files simultaneously. Often supports RAID for data redundancy.
Comparison Table
| Feature | SSD | HDD | Optical | Flash Drive | NAS |
|---|---|---|---|---|---|
| Speed | Very fast | Moderate | Slow | Moderate | Varies |
| Capacity | Up to 8 TB | Up to 20 TB | 700 MB - 50 GB | 8 - 256 GB | Multi-TB |
| Cost/GB | High | Low | Medium | Medium | Medium |
| Durability | High | Lower | Medium | High | High |
| Portability | Medium | Medium | High | Very high | Low |
| Noise | Silent | Audible | Audible | Silent | Varies |
| Moving parts | No | Yes | Yes | No | Depends |
Worked Examples
Storage Selection Matrix
For each scenario, evaluate the requirements and recommend the most appropriate storage solution.
Scenario 1: School File Server
Requirements: Large capacity, network access for staff and students, reliability, budget-conscious.
Analysis: Many users need simultaneous access, ruling out single external drives. Budget constraints favour cheaper per-GB storage. Reliability is critical for school records.
Recommendation: NAS with HDDs. The NAS provides network access for multiple users. HDDs offer large capacity at low cost. RAID configuration provides redundancy in case a drive fails.
Scenario 2: Student Laptop
Requirements: Fast boot and application loading, durability for daily transport, reasonable capacity for schoolwork.
Recommendation: SSD (256 GB - 512 GB). Fast read/write speeds make the laptop responsive. No moving parts mean it survives being carried in a backpack. 256-512 GB is sufficient for most student workloads.
Scenario 3: Photographer Backup
Requirements: Large capacity for RAW photo files (each 25-50 MB), portable for travel, affordable for bulk storage.
Recommendation: External HDD (2-4 TB). Provides massive capacity at low cost. Portable enough for travel. The sequential nature of backup writes suits HDD performance. For critical work, a second backup drive is advisable.
Scenario 4: Field Researcher
Requirements: Extreme durability (dust, moisture, drops), compact size, no external power needed, quick data transfer to lab computers.
Recommendation: Rugged flash drive or rugged external SSD. Flash drives are the most compact and require no power beyond the USB port. Rugged SSDs offer more capacity with similar durability. Both use flash memory with no moving parts, making them resistant to physical damage.
Quick Code Check
Q1. Which storage type has no moving parts?
Q2. Which storage type is the cheapest per GB for bulk storage?
Q3. What does NAS stand for?
Q4. Which storage device uses magnetic platters to store data?
Q5. Why is eMMC not ideal for high-performance computing?
Spot the Error
A student wrote the following comparison of storage technologies for a homework assignment. One statement contains a factual error. Click the line with the error, then pick the correct fix.
Pick the correct fix for the error:
Fill in the Blanks
Complete this summary comparing different secondary storage technologies. Fill in each blank with the correct term.
Secondary Storage Comparison
============================
An SSD uses flash memory and has moving parts.
An HDD uses platters that spin with a read/write head.
A is the most portable form of storage.
A allows multiple users on a network to access shared files.
Optical discs are read using a .
Secondary storage is , meaning data is retained when the power is off.Predict the Output
A video production company has these requirements for their new storage system:
Requirements:
- 10 TB of total storage capacity
- Multiple video editors must access files simultaneously over the network
- Data must survive a single drive failure without data loss
- Budget is limited — cost per GB matters
Question: Which storage solution is most appropriate?Type the name of the storage solution (three-letter abbreviation):
The key requirements are network access (multiple simultaneous users) and data redundancy (surviving a drive failure). NAS with RAID is the only option that satisfies both. RAID (Redundant Array of Independent Disks) distributes data across multiple drives so that if one fails, the data can be reconstructed from the remaining drives.
Practice Exercises
Core
-
SSD vs HDD Comparison — Compare SSD and HDD across five criteria: speed, cost per GB, durability, capacity, and noise. Present your answer as a table and write one sentence stating which you would recommend for a student laptop, with justification.
-
External Storage Examples — List three different types of external storage. For each one, give a specific real-world use case explaining why that storage type is the best fit for that scenario.
-
Why Secondary Storage? — Explain why secondary storage is necessary even though RAM exists. Your answer should address at least three reasons, referencing the concepts of volatility, capacity, and cost.
Extension
-
School Computer Lab Decision — A school is setting up a new computer lab with 30 machines. The IT budget allows either SSDs (256 GB each) or HDDs (1 TB each) for the same total cost. Write a recommendation evaluating both options. Consider: boot time, application loading, storage capacity per student, durability in a school environment, and long-term maintenance. Justify your final recommendation.
-
Cloud vs Local Storage — Evaluate the advantages and disadvantages of cloud storage compared to local secondary storage. Consider: accessibility, cost model (subscription vs one-time), internet dependency, security, scalability, and data sovereignty. Under what circumstances would you recommend each?
Challenge
- Complete Storage Solution Design — Design a storage solution for a media production company with these requirements:
- Fast editing drives for 20 video editors working with 4K footage
- Archive storage for 50 TB of completed projects
- Portable drives for 5 field crews shooting on location
- All 20 office editors need network access to current projects
- The company cannot afford to lose any project data
For each requirement, recommend a specific storage technology, justify your choice, and explain how the components work together as a complete system.
Connections
- Prerequisites: Primary Memory — secondary storage sits at the bottom of the memory hierarchy, below cache and RAM
- Related: Compression — compression reduces the amount of secondary storage needed for files
- Related: Cloud Computing — cloud storage is an alternative to local secondary storage, hosted on remote servers
- Forward: File Processing (Programming Layer) — reading from and writing to files uses secondary storage as the persistent medium