Choosing hardware starts from the job, not the biggest numbers: work out what the job needs most, compare the options on that, weigh the trade-offs, and spend the budget where the bottleneck is.
Two computers cost about the same. One has twice the cores, the other four times the RAM. Which is better?
There is no best computer, only the best one for a job. Choosing hardware means working out what the job needs most, comparing the options on that, and weighing what each choice costs.
Predict: Read the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
Try: Try it on the board and compare the result with your prediction.
Investigate: Work out why it happens, one step at a time.
Modify: Change the problem on purpose and see what happens.
Practise: A few on your own, to check you have it.
Make: Make your own problem using what you have learned. Expect a few tries; that is normal.
Make your prediction first. Help opens once you've locked it in.
PredictRead the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
A or B?
TryTry it on the board and compare the result with your prediction.
Try: run both
Was your prediction right?
Try it yourselfYour edits are saved in this browser.
Run the export on Option A and on Option B. Which is faster, and what is each one's slowest part?
Use the board. This ticks when you get there.
InvestigateWork out why it happens, one step at a time.
Worked example: four steps to a choice
Worked exampleBefore each step, say what you think comes next.
1. What does the job need?The export uses up to 8 cores and needs 16 GB of RAM.
2. Compare on thatA: 50 s processor + 8 s swapping + 3 s = 61 s. B: 100 s + 3 s = 103 s.
3. Weigh the trade-offsA is short of RAM (it swaps); B has RAM it can't use but half the cores.
4. JustifyChoose A: the processor is the export's bottleneck. Add RAM to 16 GB if the budget allows: 53 s.
Now work out A with 16 GB.
Option A with its RAM raised from 8 GB to 16 GB (costs $60 more). How many seconds is the export now?
Sam chooses a computer for video editing. Click the line where it first goes wrong.
ModifyChange the problem on purpose and see what happens.
Vary: change the job
Try it yourselfYour edits are saved in this browser.
PractiseA few on your own, to check you have it.
Choose for the job
MakeMake your own problem using what you have learned. Expect a few tries; that is normal.
The media lab
Then: write one sentence a parent could read: which computer, and why.
Try it yourselfYour edits are saved in this browser.
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.
Use the board. This ticks when you get there.
For teachers
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). About 45 minutes.
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.
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
A student picks the option with the bigger numbers (Sam's mistake). Ask: Which part is this job's slowest? Fix: Compare the options on that part.
A student is over budget and stuck. Ask: Which parts did you upgrade that aren't on the red bar? Fix: Take the money back from those.
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 ___.
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).
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.
Now you can
Choose hardware for a job and justify it with specs.
Explain a trade-off between two specs (more RAM or a faster processor).
Stay within a budget by spending on the bottleneck.