Storage Devices & Media
Where does data live when the power is off, and how do we choose the right storage?
- Distinguish primary from secondary storage, and volatile from non-volatile memory
- Classify storage by technology: magnetic, optical, solid-state and cloud
- Compare storage options by capacity, speed, portability, durability and cost
Overview
Storage keeps data and programs so they can be used again. Primary storage (RAM and cache) is fast but volatile — it forgets everything at shutdown. Secondary storage (hard disks, SSDs, flash drives, memory cards, optical discs and cloud services) is non-volatile and holds your files permanently. Understanding units of capacity and the trade-offs between storage types is essential for buying, backing up and troubleshooting.
Primary vs secondary storage
Primary storage sits close to the CPU: registers and cache (tiny and extremely fast), then RAM (fast, volatile, holds what is running now), plus ROM/firmware which is read-only and keeps the start-up instructions. Secondary storage is larger, slower, cheaper per gigabyte and non-volatile.
Units of storage capacity
Data is measured in bits and bytes: 8 bits = 1 byte; 1,024 bytes = 1 KB; 1,024 KB = 1 MB; 1,024 MB = 1 GB; 1,024 GB = 1 TB. A page of text is a few KB, a photo a few MB, an HD movie several GB.
Storage technologies compared
Four families cover almost all storage in use today.
Compare these types:
- Magnetic — HDD: Spinning platters and a read/write head. Large capacity (1–8 TB+) and cheap per GB, but slower and easily damaged by knocks. Also magnetic tape, still used for cheap long-term backup.
- Solid-state — SSD, flash drive, memory card: Flash memory chips with no moving parts. Much faster, silent and shock-resistant; higher cost per GB. Includes USB flash drives, SD/microSD cards and internal NVMe SSDs.
- Optical — CD, DVD, Blu-ray: A laser reads pits on a disc. Cheap and long-lasting for distribution and archiving; small capacity (CD 700 MB, DVD 4.7 GB, Blu-ray 25 GB+) and increasingly rare on new machines.
- Cloud & network storage: Files stored on remote servers (Google Drive, OneDrive) or a local file/NAS server. Accessible from anywhere and easy to share, but depends on internet bandwidth and cost — a real constraint in much of Papua New Guinea.
Choosing storage: the five trade-offs
Compare capacity (how much), speed (how fast to read/write), portability (can you carry it), durability/reliability (will it survive heat, dust and drops), and cost per gigabyte. An SSD makes a laptop feel new; an external HDD is the cheapest way to back up 2 TB of school data; a microSD card is the most portable.
Backup and care
Follow the 3-2-1 rule: three copies of important data, on two different media, with one copy off-site (for example an external drive kept at home plus a cloud copy). Eject flash drives safely, keep discs out of direct sunlight, and never move a running HDD.
Storage comparison table + backup plan
- Build a table with columns: Device | Technology | Typical capacity | Speed | Portability | Cost per GB | Best use.
- Fill in rows for: internal HDD, internal SSD, USB flash drive, microSD card, DVD, external HDD, cloud storage.
- Convert: 5 GB to MB; 2,048 MB to GB; 16 bits to bytes.
- Then write a 3-2-1 backup plan for your school's student records, naming the exact media you would use.
- State two differences between primary and secondary storage.
Reveal answer
Primary is fast and (for RAM) volatile and small; secondary is slower, non-volatile and much larger.
- How many MB are in 3 GB?
Reveal answer
3 × 1,024 = 3,072 MB.
- Give one advantage and one disadvantage of an SSD over an HDD.
Reveal answer
Advantage: much faster and shock-resistant. Disadvantage: costs more per gigabyte.
- Why is cloud storage sometimes a poor choice in rural PNG?
Reveal answer
It depends on internet bandwidth and data cost, which may be slow, unreliable or expensive.
- Explain the 3-2-1 backup rule.
Reveal answer
Keep three copies of the data, on two different types of media, with one copy stored off-site.
Price a 1 TB external hard drive and 1 TB of cloud storage for a year in PNG. Which is better value for your school, and why?