You take the Unit 1 test in class today. This page is everything you can do before it — what is on it, how to revise, and a practice set. There are no test questions here.
No new reading. Everything on the test comes from lessons 1.1–1.13. The fastest revision is the drill in 1.13, not re-reading.
Last stop in Bits. The test is not a new idea — it is a checkpoint on the three weeks behind you. Tomorrow, in 1.15, you get the test back and we move on to Programs.
The fifteen multiple-choice questions are spread across the unit in roughly these proportions. This is the map of where the points are — study to it.
| What it tests | From | Roughly |
|---|---|---|
| Binary ↔ decimal conversion | 1.1, 1.2 | 3–4 Q |
| How many values in n bits / largest value | 1.1, 1.3 | 2 Q |
| Overflow vs round-off (which failure is which) | 1.3 | 2–3 Q |
| Text as bits — ASCII and Unicode | 1.4 | 2 Q |
| Images — pixels, RGB, counting bits per pixel | 1.5 | 1–2 Q |
| Analog vs digital, sampling | 1.6 | 1–2 Q |
| Compression — lossless vs lossy, and choosing | 1.8, 1.9 | 2 Q |
| Abstraction used correctly in context | 1.7 | 1 Q |
Re-reading the lessons feels productive and mostly isn’t. Retrieval — making yourself produce the answer before you check — is what actually moves a grade. Here is the order that pays off fastest:
1. Say the unit in one breath (2 min). Out loud: “how does the world turn into bits, and what goes wrong on the way?” If you stall, you just found tonight’s study target.
2. Run the five traps (5 min). Below. These are the pairs that actually cost marks.
3. Drill conversions cold (5 min). Open the practice tools and do binary↔decimal until three in a row are automatic.
4. Take the practice set (8 min). Section 4 on this page — fresh questions, none of them on the real test.
Every one of these has shown up on a real exam. Thirty seconds each:
| Don’t confuse | The one-line difference |
|---|---|
| bit vs byte | A bit is one 0 or 1. A byte is 8 of them — so a count in bits is bigger. |
| 2n vs 2n−1 | 2n is how many patterns. 2n−1 is the largest value, because 0 uses one up. |
| overflow vs round-off | Overflow = the number was too big (sudden wrong value). Round-off = too precise (slow drift). |
| analog vs digital | Analog is continuous. Digital is a finite set of discrete values. |
| lossless vs lossy | Lossless gives the original back exactly. Lossy does not, ever. |
Want the interactive version of all this? Lesson 1.13 has the map-rebuild puzzle and a drill on all 22 vocabulary terms. That is the single best 15 minutes of revision on the site.
Six mixed questions in AP format, sampled across the whole unit. None of these is on the real test — they are for calibration. Pick an answer to see feedback immediately.
Prompt. A hospital stores X-ray images so that radiologists can examine them for hairline fractures. Storage space is limited, and someone suggests compressing the images to fit more of them. Should the hospital use lossless or lossy compression here? Justify your answer, and use the word lossy correctly in your explanation.
Write three or four sentences before you open the checklist below.
□ Picks a side clearly. Lossless. (Saying “it depends” without committing earns nothing.)
□ Names the tradeoff. Lossy compression permanently discards data to save space; lossless keeps every bit and reconstructs the original exactly.
□ Ties it to this situation. A hairline fracture might be a few faint pixels. Lossy compression could throw exactly those away, changing a diagnosis — so the space saving is not worth the risk here.
□ Uses the term correctly. “Lossy would discard detail that cannot be recovered” — not just the word dropped in a sentence.
The recurring skill the AP written responses reward is refusing to over-claim. Don’t write “lossy is always bad.” Write “lossy is the wrong choice here, because…” The word here is worth a point.