30 practice questions for the midterm, covering:

• Number conversions (Part A)
• Structure of a computer, files & paths (Part B)
• Text files & Git (Part C)
• Large language models (Part D)
• Boolean logic (Part E)

Show your work on the conversion questions, exactly like the homework.

Part A — Number Conversions

#

Q1. Convert the decimal number 37 to binary using repeated division.

Q2. Convert the decimal number 53 to binary by repeatedly subtracting the largest power of two.

Q3. Convert the binary number 11010 to decimal.

Q4. Convert the decimal number 200 to hexadecimal.

Q5. Convert the hexadecimal number 7B to decimal.

Q6. Convert the decimal number 90 to octal.

Q7. Convert the octal number 52 to decimal.

Q8. Convert the binary number 11101001 to hexadecimal.

Q9. Convert the hexadecimal number F4 to binary.

Q10. Convert the decimal number 13.75 to binary (do the whole part and the fractional part separately).

Q11. Convert the binary number 1010.101 to decimal.

Q12. Convert the decimal number -9 into 8-bit two’s complement binary.

Q13. The 8-bit two’s complement number 11110110 represents which decimal number?

Q14. Decode the single-precision IEEE 754 value 0 10000010 01000000000000000000000 to decimal.

Part B — Structure of a Computer, Files & Paths

#

Q15. List four main parts of a computer and give a one-line description of each. (This is a terrible question, but I might ask what RAM is.)

Q16. (a) While a program is running, where is its data kept? (b) If you want that data to still be there after the program exits, where does it go?

Q17. Fundamentally, what is a file made of? Besides its contents, what kind of extra information (metadata) does a file have?

Q18. (a) What character does an absolute path start with on Linux and macOS? (b) What does it start with on Windows? (c) What character separates the parts of a path on Linux?

Q19. Your terminal’s working directory is /home/alice/docs. (a) What is the absolute path of the file ../notes/todo.txt? (b) What does .. mean, and what does . mean?

Q20. Compare a GUI and a CLI: give one advantage of each.

Part C — Text Files & Git

#

Q21. In one sentence, what is a text file? Then: how many bytes long is the text Hello, CS 2010 when stored as ASCII?

Q22. (a) How many bits is ASCII? (b) If we really use 8 bits per character, how does the computer tell an ASCII character from a non-ASCII one?

Q23. What is UTF-8, and why was it invented? Roughly how many bytes does each of these take: an ASCII character, a character from most other alphabets, a CJK/Hangul character, and an emoji?

Q24. Define each of these Git terms: repository, commit, push, clone.

Q25. Give two reasons to use version control. Then describe the basic collaborative GitHub workflow (branch → change → commit → push → pull request).

Part D — Large Language Models

#

Q26. In one sentence, what does a large language model do? What is a token?

Q27. Why can’t you run the very largest LLMs on a normal laptop? In your answer, mention weights and quantization.

Part E — Boolean Logic

#

Q28. Fill in the truth tables for AND, OR, and NOT.

Q29. Evaluate (A AND B) OR (NOT A) for A = 1, B = 0. Show your steps.

Q30. A lamp is controlled by two switches and should be ON if exactly one switch is on (and OFF otherwise). Write a truth table and a boolean expression for this.

Answer Key

#

Part A

#

Q1. 37 → binary

• 37 / 2 = 18 r 1
• 18 / 2 = 9 r 0
• 9 / 2 = 4 r 1
• 4 / 2 = 2 r 0
• 2 / 2 = 1 r 0
• 1 / 2 = 0 r 1

Remainders in reverse: 100101 (check: 32 + 4 + 1 = 37 ✓)

Q2. 53 → binary (subtract largest power of two)

• 32 ≤ 53 → 1, 53 − 32 = 21
• 16 ≤ 21 → 1, 21 − 16 = 5
• 8 > 5 → 0
• 4 ≤ 5 → 1, 5 − 4 = 1
• 2 > 1 → 0
• 1 ≤ 1 → 1, 1 − 1 = 0

Answer: 110101 (check: 32 + 16 + 4 + 1 = 53 ✓)

Q3. 11010 = 16 + 8 + 0 + 2 + 0 = 26

Q4. 200 → hex

• 200 / 16 = 12 r 8
• 12 / 16 = 0 r 12 = C

Remainders in reverse: C8 (check: 12 × 16 + 8 = 200 ✓)

Q5. 7B = 7 × 16 + 11 = 123

Q6. 90 → octal

• 90 / 8 = 11 r 2
• 11 / 8 = 1 r 3
• 1 / 8 = 0 r 1

Remainders in reverse: 132 (check: 1 × 64 + 3 × 8 + 2 = 90 ✓)

Q7. 52 (octal) = 5 × 8 + 2 = 42

Q8. 11101001 → group into nibbles: 1110 1001 = E9

Q9. F4 → each hex digit is 4 bits: F = 1111, 4 = 0100 → 11110100

Q10. 13.75 → binary

• Whole part, 13: 13 / 2 = 6 r1; 6 / 2 = 3 r0; 3 / 2 = 1 r1; 1 / 2 = 0 r1 → reverse → 1101
• Fractional part, 0.75: 0.75 × 2 = 1.5 → digit 1; 0.5 × 2 = 1.0 → digit 1 → in order → .11

Answer: 1101.11 (check: 8 + 4 + 1 = 13, and 0.5 + 0.25 = 0.75 ✓)

Q11. 1010.101

• Whole: 8 + 2 = 10
• Fraction: 1/2 + 1/8 = 0.5 + 0.125 = 0.625

Answer: 10.625

Q12. −9 in 8 bits: +9 = 00001001; flip → 11110110; add 1 → 11110111

Q13. 11110110 is negative. Flip → 00001001; add 1 → 00001010 = 10, so the value is −10

Q14. 0 10000010 01000000000000000000000

• Sign = 0 (positive)
• Exponent = 10000010₂ = 130; real exponent = 130 − 127 = 3
• Fraction = 0100… = 1/4, so mantissa = 1.25
• Value = 1.25 × 2³ = 1.25 × 8 = 10.0

Part B

#

Q15. The four main parts:

• CPU — runs the program / does the computation.
• RAM — fast, temporary working memory while the computer is on.
• Disk — slow, persistent storage that survives power-off.
• I/O — input/output devices: keyboard, screen, network, etc.

Q16. (a) In RAM (main memory). (b) On disk, in a file.

Q17. A file is a series of bytes (its contents) plus a name and some metadata (size, dates, maybe a type).

Q18. (a) A forward slash /. (b) A drive letter such as C:. (c) /.

Q19. (a) /home/alice/notes/todo.txt. (b) .. means the parent directory (the directory one level up). . means the current directory.

Q20. GUI — common actions are visual and discoverable; good for casual use. CLI — a language of commands, so it is more powerful and scriptable, but you have to know the commands.

Part C

#

Q21. A text file is a file whose bytes are meant to be read as characters of text (rather than, say, image or audio data). Hello, CS 2010 is 14 bytes (one byte per ASCII character).

Q22. (a) ASCII is 7 bits (128 possible characters). (b) We store each character in a byte: if the top bit is 0, the remaining 7 bits are an ASCII code; if the top bit is 1, the byte is part of a multi-byte (non-ASCII) character.

Q23. UTF-8 is a variable-length encoding of Unicode (invented by Ken Thompson) that keeps ASCII text unchanged. It was invented so that old 8-bit/ASCII tools would still work while the full Unicode set was supported. Sizes: ASCII = 1 byte; most other alphabets = 2 bytes; CJK/Hangul = 3 bytes; rare/historical characters and emoji = 4 bytes.

Q24.

• Repository — a project whose files and full change history Git is tracking.
• Commit — a saved snapshot of your changes, with a message, stored locally.
• Push — send your local commits up to a remote (e.g. GitHub).
• Clone — make a local copy of a remote repository on a new machine.

Q25. Two reasons: (1) tracking changes over time (history, ability to see/undo what changed), and (2) multi-user collaboration. Workflow: make a branch, make a change, commit it, push the branch, then open a pull request so it can be reviewed and merged.

Part D

#

Q26. An LLM predicts the next token given the previous tokens, then appends that token and repeats. A token is a chunk of text (roughly a word or symbol) represented by a number.

Q27. To generate each token, the model must do math using all of its weights, so the weights have to fit in fast memory (VRAM/RAM). The biggest models have trillions of weights, which would need far more memory than a laptop has. Quantization stores each weight with fewer bits (16 → 8 → 4) to shrink the model so it fits, at some cost in quality.

Part E

#

Q28.

Q29. (A AND B) OR (NOT A) with A = 1, B = 0:

• A AND B = 1 AND 0 = 0
• NOT A = 0
• 0 OR 0 = 0

Q30. Truth table (1 = on):

Expression: (A AND NOT B) OR (NOT A AND B) — this is XOR.