Multiple Choice Questions

Answer all questions. Select an option to get instant feedback.

Answered: 0 / 0
Q 1 of 0

Question Navigator

Fill in the Blanks

Click a word in the pool to move it to the first empty blank. Click a filled blank to return the word.

Total Answered: 0 / 0

Creative Activities

Interactive challenges: conversions, tracing, puzzles, and debugging exercises.

Completed: 0 / 0

Short Answer Questions (1-3 Marks)

Review model answers and mark schemes for Cambridge IGCSE CS 0478.

Long Answer Questions (3-6 Marks)

Write detailed answers and trace calculations. Compare against model answers.

Key Takeaways

Essential concepts, definitions, and common exam pitfalls for Chapter 3.1: Hardware.

CIE Command Word Decoder

Understanding command words is critical for exam success. Each word requires a different depth of response.

STATE / IDENTIFY

Brief, factual answer — no explanation needed

1State the denary value of binary 1010
  • 10  (8 + 2)
2State the number of bits in one nibble
  • 4 bits  (half a byte — one hexadecimal digit)
3State the number of values that can be represented using 4 bits
  • 16  (2⁴ = 16 possible values, 0–15)
4Identify the hex digits used in the hexadecimal system
  • 0–9 and A–F  (16 symbols total)
5State what BCD stands for
  • Binary-Coded Decimal

DESCRIBE

Say what happens or how it works (what / how)

1Describe how to convert denary to hexadecimal
  • Divide the denary number by 16
  • The quotient gives the first hex digit, the remainder gives the second
  • Alternatively, convert to binary first, then split into nibbles
2Describe how to convert a hexadecimal number to binary
  • Expand each hex digit into its 4-bit nibble
  • Join the nibbles in the same order (A3 → 1010 0011)
3Describe how two's complement represents negative numbers
  • The most significant bit (leftmost) is the sign bit: 0 for positive, 1 for negative
  • To find the two's complement: flip all bits and add 1
  • Range in 8 bits is −128 to +127
4Describe the process of a binary left shift
  • Each shift moves all bits one position to the left
  • The rightmost bit is filled with 0
  • This multiplies the value by 2 for each shift position
5Describe what happens to bits shifted beyond the end of the register in a logical shift
  • Bits shifted beyond the end of the register are lost
  • Zeros are shifted in at the opposite end
  • A lost 1 bit means the stored value is now wrong (data loss)

EXPLAIN

Give reasons — say why something happens

1Explain why overflow occurs in 8-bit addition
  • When the sum of two numbers exceeds 255 (the maximum 8-bit value), a 9th bit is needed
  • Since only 8 bits are available, this carry bit is lost
  • This gives an incorrect result
2Explain why BCD wastes storage space
  • BCD uses 4 bits per denary digit
  • 4 bits can represent 16 values (0–15), but only 0–9 are used
  • Digits above 9 (1010–1111) are unused
  • So 6 out of 16 combinations are wasted per digit
3Explain why hexadecimal is used as a shorthand for binary
  • One hex digit maps exactly to one 4-bit nibble (2⁴ = 16)
  • Each byte (8 bits) is represented by exactly 2 hex digits
  • This makes long binary values much shorter and easier for humans to read
4Explain why memory dumps are shown in hexadecimal rather than binary
  • Each hex digit represents exactly 4 bits, so values are much shorter
  • 8 hex digits replace 32 binary bits — far easier to read and trace
  • This makes it easier for programmers to locate where the error lies
5Explain why an overflow error can occur when adding two 8-bit binary numbers
  • The result may need a 9th bit (e.g. 255 + 1 = 256)
  • An 8-bit register has a predefined limit it can represent
  • The carry is lost, so the stored result is incorrect

EVALUATE / DISCUSS

Weigh up pros and cons with a justified conclusion

1Discuss the advantages of writing error codes in hexadecimal rather than binary
  • Hex is far shorter — one hex digit replaces 4 bits
  • Fewer digits mean fewer transcription errors when reporting codes
  • However, the computer still processes pure binary — hex is only a human shorthand
2Evaluate the use of BCD in financial systems
  • BCD avoids rounding errors that occur in binary floating-point when representing decimal fractions (e.g. 0.1)
  • This precision is critical for currency calculations
  • The trade-off is wasted storage (6 unused patterns per nibble)
  • BCD arithmetic is also slower than pure binary
3Discuss whether it is better to store numbers in binary or BCD
  • Pure binary uses storage more efficiently and allows faster arithmetic
  • BCD avoids decimal conversion errors
  • BCD is easier to display on 7-segment displays
  • Binary is better for general computation; BCD is better for financial accuracy
4Evaluate the use of two's complement for representing signed integers
  • There is only one representation of zero, and addition works with the same circuitry
  • However, the range is fixed (−128 to +127 in 8 bits), so overflow is possible
  • The MSB carries weight −128, which must be handled correctly in conversions
5Discuss the limitations of using 8-bit two's complement for integer storage
  • 8-bit two's complement is limited to −128 to +127
  • This narrow range causes overflow in even moderate calculations
  • Larger integers require more bits (16, 32, 64), increasing memory usage
  • The choice depends on the range needed by the application