Students compare two computers on different jobs, follow four steps to a justified choice, and build the cheapest computer that meets a media-lab brief within a budget (AC9TDI8K01 node 3).
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Students will be able to
I can choose hardware for a job and justify it with specs.
I can explain a trade-off between two specs (more RAM or a faster processor).
I can stay within a budget by spending on the bottleneck.
Timing
Predict and Try 7 min · Worked example 10 min · Vary 8 min · Practise 8 min · Make 12 min
Before class
Try the boards yourself.
The one idea: choose for the job. Scaffold the reasoning with the four steps (what the job needs, compare on that, weigh the trade-offs, justify) on the board all lesson.
Prices on the board are made up but in proportion, and the cheapest Make answer is 8 cores at 3.0 GHz, 16 GB RAM and a 1 TB SSD ($780, 53 s); 8 cores at 4.0 GHz is $900 and 41 s. Real prices change; the Digital Technologies Hub suggests comparing specs in an online computer store, which works well as an extension.
The same Option A versus B comparison gives different winners for different jobs; that is the point of Vary.
Running the lesson
Predict: students who chose B hold Sam's misconception; Try settles it.
Try: ask why B's extra RAM did nothing for the export.
Worked example: model the four steps aloud, then ask where the $60 for RAM went.
Vary: ask why the game load is a tie.
Make: collect the cheapest working builds on the board and compare the justifications.
The hard part (on purpose)
The Make has no single obvious answer and the budget pushes back. Let students run, overspend and adjust; the four steps are the scaffold, not the teacher.
When students get stuck
What you will see
A question to ask
The fix
A student picks the option with the bigger numbers (Sam's mistake).
Which part is this job's slowest?
Compare the options on that part.
A student is over budget and stuck.
Which parts did you upgrade that aren't on the red bar?
Take the money back from those.
Answers to the checks
A or B?: For exporting video, Option A has 8 cores and 8 GB of RAM; Option B has 4 cores and 32 GB of RAM. Both cost about $700. Which exports faster? Option A: 61 seconds against B's 103. The export needs processor power most; A swaps a little, but its cores matter more.
Try: run both: Run the export on Option A and on Option B. Which is faster, and what is each one's slowest part?
A: 61 s, slowest part the processor (plus a little swapping). B: 103 s, the processor: 32 GB of RAM doesn't help when 16 GB is enough.
Video editing, step by step: Option A with its RAM raised from 8 GB to 16 GB (costs $60 more). How many seconds is the export now? 53 Processor 1200 ÷ (8 × 3) = 50 s, storage 3 s, no swapping: 53 s, for $780.
Find the mistake: Sam chooses a computer for video editing. Click the line where it first goes wrong. line 3 Line 3: a bigger number only helps if that part is the job's bottleneck. For exporting video it is the processor, so A is the better choice.
A different job: Same two options, but the job is keeping 30 browser tabs open. Which is better? Option B: tabs need RAM, and A has to swap B: 2 s against A's 6 s. A different job, a different best choice.
Tabs: Run the tabs job on both. Which option wins? Option B B: no swapping. For lots of tabs, RAM matters most.
Game: Run the game load on both. Which option wins? They tie: both have the same SSD, which is the bottleneck Both 7.3 s. When the bottleneck is a part they share, their differences don't matter.
Download: Run the download on both. What would actually help? A faster network, on either option Both take about 800 s at 50 Mb/s: the network is the bottleneck.
A school laptop: A Year 8 student's laptop: web browsing, documents and video calls. Where should the money go? Enough RAM (about 8–16 GB), an SSD and good Wi-Fi Tabs need RAM, starting and opening need an SSD, calls need the network.
AI: A computer for training AI models. Which one part matters most? A graphics card Training is millions of small sums: a graphics card does thousands at once.
A file server: A school file server where 1,000 students save and open work. Which pair matters most? Lots of storage and a fast network Everyone's files have to fit, and many people send and fetch them at the same time.
Review: bottlenecks: Review: a laptop with a hard disk takes 2 minutes to start up. What is the bottleneck? Storage speed Starting up reads programs from storage: an SSD fixes it.
Build it: The school media lab needs computers that export the video in under 60 seconds, hold at least 1 TB of footage, and cost no more than $900. Build one from the old laptop and run the export.
For example 8 cores at 3.0 GHz, 16 GB of RAM and a 1 TB SSD: 53 s for $780. Each dollar went to the job's bottleneck.
Solutions
One possible solution for each task. Other correct programs are fine.
Vary: change the job › Tabs
Open task: any program that does what the step asks.
Vary: change the job › Game
Open task: any program that does what the step asks.
Vary: change the job › Download
Open task: any program that does what the step asks.
the media lab › Build it
Open task: any program that does what the step asks.
the media lab › Justify it
Open task: any program that does what the step asks.
Stretch and support
Stretch: A school can rent time on a cloud server instead of buying 30 media-lab computers. When would that be the better choice?
Support: The four steps as a card with blanks: The job needs ___. Option ___ is better at that. The trade-off is ___. I choose ___ because ___.
Exit ticket
Two laptops cost the same. One has more RAM, the other a faster processor. Which would you choose for a student who keeps many tabs open, and why?
The one with more RAM: many tabs need working space, and too little RAM swaps to storage. The faster processor wouldn't fix that.
What each step is for
A or B?: Committing to an option for video editing tests the new move, choose by the job's bottleneck, before students run both.
Try: run both: Running the export on both options settles the prediction: the job's bottleneck, not the biggest number, decides.
Worked example: four steps to a choice: Following the four steps (what the job needs, compare on that, weigh the trade-offs, justify) models the new move. Sam picks the biggest number, the misconception planted after the method.
Vary: change the job: Each task keeps the two options and changes one thing, the job, so the best choice changes with it, including jobs where neither option wins.
choose for the job: Choosing for described jobs without the board is the same move in mixed forms, plus a review of finding the bottleneck.
the media lab: Building the cheapest computer that meets a brief reverses the process: start from the job, the target and the budget, choose the parts, then justify the choice.
Where it leads
Next in Digital systems: Networks (bandwidth and packets) or Security and privacy (Years 9–10).
Links: Engineering › Physical computing (choosing a board for a project).