Caching

Definition

Caching is a technique used to store frequently accessed data or instructions in a special memory (cache) for quick retrieval. The goal is to reduce access time from slower storage mediums, thereby improving overall system performance.

Benefits of Caching

Key Point

Caching benefit	Why it helps
Speed	Cache access is far faster than secondary storage access
Efficiency	Reuses frequent data instead of repeatedly fetching from slow storage
Reduced load	Lowers pressure on databases/disks and network resources

Drawbacks of Caching

Key Point

Caching drawback	Why it is a problem
Cache size limits	Small caches cannot hold all useful data; very large caches add lookup overhead
Implementation complexity	Cache policies/prefetching are hard to tune correctly
Data consistency risk	Cached data can become stale if source data changes
Cache misses	Misses force slow fallback to main/secondary storage

Worked Example

Worked Example: Web Browser Caching

Step	What happens
1	User visits www.example.com
2	Browser downloads HTML/CSS/images
3	Browser stores these files in local cache
4	User revisits the page
5	Browser serves cached files (if valid) instead of re-downloading

Benefit: faster page load and reduced bandwidth/server demand.

Potential problem: stale content may be shown until cache expiry/refresh.

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Question

Caching

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Answer

Storing data or instructions that have already been used in a location that can be accessed quickly, such as RAM, in case they are needed again, so that later retrieval is faster.

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Browse all 4 flashcards on The Nature, Benefits, and Drawbacks of Caching

Caching
Storing data or instructions that have already been used in a location that can be accessed quickly, such as RAM, in case they are needed again, so that later retrieval is faster.
Benefits of Caching
Data needed again is read from fast memory instead of being fetched again from secondary storage or over a network, so access is faster, the program performs better and less bandwidth and processor time is used.
Drawbacks of Caching
Keeping copies of used data only helps if the same data is requested again. The copies take up memory and may become out of date, and the technique is more complicated to design and implement, adding development time.
Web Caching Example
A browser keeps copies of a site's images, style sheets and scripts on the local device, so that on a return visit they load from local storage instead of being downloaded again: the page appears sooner and less bandwidth is used.

Exam questions on The Nature, Benefits, and Drawbacks of Caching

3 OCR past paper questions (22 marks) with mark schemes

Question 1H446/02 · June 20199 marks
A program is needed to plan the layout of a garden. The programmer is designing the program to make use of caching and re-useable components. Explain and evaluate the use of caching and re-useable components in the design of the garden program.
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Levels of response (9 marks) Caching: Storing frequently used data for quick access. Garden program could cache: plant images, common layouts, user preferences. Benefits: faster loading, reduced computation. Drawbacks: memory usage, stale data. Re-useable components: Modular code used multiple times. Garden program: plant object class, resize function, positioning tools. Benefits: faster development, consistent behavior, easier maintenance. Drawbacks: may not fit all cases perfectly.
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Question 2H446/02 · June 20189 marks
Kamran wants to expand a program to handle up to 100,000,000 items and allow searching. Evaluate the use of caching and concurrent processing in this scenario and make a recommendation.
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Levels of response (9 marks) Caching: Store frequently accessed items in memory. Reduces disk reads. Cache hit = fast access. Consider cache size vs memory. LRU or LFU policies. Concurrent processing: Multiple threads searching simultaneously. Divide data into partitions. Reduces search time. Need to manage thread safety. May have diminishing returns. Recommendation: Use both together for optimal performance. Cache for frequent queries, concurrent processing for large searches.
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Question 3H446/024 marks
Describe what is meant by caching and explain how caching can be used within an accident and emergency room simulation to train hospital staff.
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Caching: Storing copies of frequently accessed data closer to where it's needed / in faster storage (1 mark) Reduces time to retrieve data (1 mark) A&E simulation use: - Cache patient scenarios that are commonly used - Store pre-rendered graphics/animations - Cache frequently used medical data/procedures - Speed up loading of common emergency situations (4 marks - 2 for definition, 2 for application)
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Benefits of Caching

Drawbacks of Caching

Exam questions on The Nature, Benefits, and Drawbacks of Caching

Past paper questions