FIFO slot replacement
Trace a three-slot store whose oldest insertion leaves on a miss.
Adult planning suggestion: about 9–12 · Logic & rule checking
- Players
- 3 per group
- Time
- 20–30 minutes
- Materials
- Printed record sheet, pencil and paper markers
Prepare
Give each group three slots, a queue strip labeled oldest→newest and requests A,B,C,A,D,B,E. The store and queue start empty. Requests are symbols, not numbers to be sorted.
Follow the rule
If a requested symbol is present, record HIT and leave the queue order unchanged. If absent, record MISS. When space remains append the symbol; when full remove the oldest queue entry first, then append the new symbol.
Check each step
The recorder writes the entire queue after every request, including hits. The checker may challenge an eviction before the next request by pointing to the insertion history. A hit is never moved to the newest end in FIFO.
Worked example
After A,B,C the queue is[A,B,C]. The next A is a hit and leaves it unchanged. D then evicts A, giving[B,C,D], although A was just requested. B is another hit; E evicts B.
Finish and adapt
Finish at the end of the seven requests and count hits and misses. Rotate roles and retry A,B,A,C,D on a fresh sheet. Do not use a second policy in the same trace; this is a paper model, not a performance claim for actual devices.
Purpose, observation and provenance
Within this activity: Trace a three-slot store whose oldest insertion leaves on a miss.
Observe whether hits preserve insertion age and the full queue is recorded.
Our rules, examples and printable diagrams are separately prepared. The earliest inventor of the broader mechanism is not established here.
OSTEP: replacement policies — Technical background, not an evaluated primary-school lesson. This paper exercise and examples are our adaptation; age and support are adult planning suggestions.
Secondary practice: Cooperation and explaining a check.
For a class of 30, use ten groups of three. Prepare one player-material set per group and keep the host key with the adult. Rotate operator, recorder and checker after each worked example; a reader or scribe may help without choosing answers. Avoid public ranking or diagnostic labels.
Age bands are planning suggestions. Background references may address older learners and do not validate suitability for this age band. Goals describe observable actions, not measured long-term gains or institutional endorsement.
Free alternative: Copy the supplied grids, labels and cards onto reused paper. No specialist product is needed. Adults may prepare pieces or act as a scribe.
Printable materials
Preview at 100% scale, with browser headers and footers off. Cut with suitable help. Keep host keys separate. This is a manual tabletop kit, not an online opponent, automatic judge or solver.
FIFO slot replacement · Player sheet
Before you begin
- Give each group three slots, a queue strip labeled oldest→newest and requests A,B,C,A,D,B,E. The store and queue start empty. Requests are symbols, not numbers to be sorted.
- If a requested symbol is present, record HIT and leave the queue order unchanged. If absent, record MISS. When space remains append the symbol; when full remove the oldest queue entry first, then append the new symbol.
- The recorder writes the entire queue after every request, including hits. The checker may challenge an eviction before the next request by pointing to the insertion history. A hit is never moved to the newest end in FIFO.
Capacity3, oldest→newest. Hits do not reorder.
| Request | HIT / MISS | Queue after |
|---|---|---|
| ________ | ________ | ________ |
| ________ | ________ | ________ |
| ________ | ________ | ________ |
| ________ | ________ | ________ |
| ________ | ________ | ________ |
| ________ | ________ | ________ |
| ________ | ________ | ________ |
FIFO slot replacement · Host key — keep separate
HIT2,MISS5; final queue C,D,E. Fresh task misses 4,hits 1; final B,C,D.
What to observe
Observe whether hits preserve insertion age and the full queue is recorded.
Use the three-person roles described in the rules; offer reading or writing support without selecting answers.
Read the rules as well as this example. Other valid solutions may exist for the puzzle boards. This key is not a claim of uniqueness or measured learning gains.
| Constraint / action | Evidence / correction |
|---|---|
| ________ | ________ |
| ________ | ________ |
| ________ | ________ |
| ________ | ________ |