Secondary storage, compression and cloud services
Choose storage and cloud models from requirements, and explain how compression changes data size and fidelity.
Choose technology from constraints, not from brand names
- describe internal and external secondary-storage types and justify them in real scenarios;
- distinguish lossy and lossless compression and describe RLE and transform coding;
- describe SaaS, PaaS and IaaS;
- compare control, flexibility, resource management and resource availability across cloud service models.
Rapid Recall Deck
Attempt each card first. If a term is new, flip and study it, then answer it again without looking. Mark only secure recall as “Know it”.
Storage scenarios reveal the trade-off
Internal device
A thin school laptop needs fast local storage with no moving parts and moderate capacity. Choose among HDD, SSD and eMMC and justify one reasonable option.
An internal SSD is a strong choice when speed and durability matter; eMMC may fit lower-cost embedded/lightweight devices, while HDD offers capacity/cost advantages but has moving parts and is generally slower.
Large local archive
A desktop stores many terabytes of rarely moved video files and cost per terabyte matters more than access speed. Choose a likely drive type.
An HDD is reasonable because high capacity at relatively low cost is more important than SSD-level access speed.
Shared network storage
Several computers need centralized shared files accessible over the local network. Which listed storage type is designed for this role?
Network attached storage (NAS) provides storage that multiple networked devices can access.
Internal/external is about system placement and use
Complete the external-storage map
Match each situation to one reasonable external storage type and justify the match. Use each option once if it fits: external SSD/HDD, optical media, memory card, flash drive.
A. long-term distribution/read-only media
B. portable transfer between computers
C. camera removable storage
D. large portable backup drive
Reasonable matches include optical media for distribution/archival use cases where optical compatibility matters; flash drive for compact file transfer; memory card for cameras/embedded devices; external SSD/HDD for large backups, with SSD favouring speed/shock resistance and HDD favouring cost/capacity.
Compression trades storage/transmission size against reconstruction
Run-length encoding
Encode AAAAABBBCCAAAA as character-count runs. Then explain when RLE is effective.
One representation is 5A3B2C4A. RLE works well when data contains long repeated runs; it can be ineffective when values change frequently because counts add overhead.
Lossy or lossless?
Choose a compression type for (A) a source-code archive and (B) a streaming photo preview where a small quality loss is acceptable. Justify each.
A: lossless, because every source-code character must be restored exactly. B: lossy can be appropriate because discarding less important information can reduce size substantially when exact reconstruction is not required.
Cloud services differ mainly in who manages which layers
SaaS
A school wants ready-to-use online email and documents with minimal server administration.
Best fit? SaaS — the provider manages the application and underlying platform.
PaaS
A team wants to build and deploy its own web application without managing operating-system patches or physical servers.
Best fit? PaaS — developers control application code while the provider manages more of the platform.
IaaS
A company needs custom virtual machines, networking and OS-level control.
Best fit? IaaS — more infrastructure control and flexibility, but more customer management responsibility.
Control and convenience move in opposite directions
Compare the cloud approaches
A startup wants rapid application development with little infrastructure maintenance, while another team needs OS-level configuration and custom networking.
The rapid-development startup is well matched to PaaS: the provider supplies a managed platform and resources while developers focus on application code. The team needing OS/network control is better matched to IaaS, accepting more administrative responsibility in exchange for flexibility. SaaS would provide the least infrastructure control because the application itself is already supplied.
Short answers still need a clear reason
Paper 1-style mini-set
1. Outline why PaaS is suitable for building applications.
2. Describe one difference between lossy and lossless compression.
3. A media studio needs a fast portable 2 TB working drive that will be moved often. Suggest a storage type and justify.
- PaaS supplies a ready managed development/deployment environment and infrastructure resources, reducing the need to administer servers/OS layers while retaining control of application development.
- Lossless permits exact reconstruction; lossy removes information and cannot reproduce the original exactly, usually in exchange for greater size reduction.
- An external SSD is reasonable because it offers fast access and no moving parts, making it suitable for frequently moved working storage.
Finish the learning cycle
IA — main task
Continue Criterion D implementation/testing and update your evidence log. Use storage/cloud decisions only if they are genuinely relevant to your solution.
Paper 1 — short practice
From memory, classify every listed secondary-storage type as internal/external, explain RLE vs transform coding, and compare SaaS/PaaS/IaaS.