AQA GCSE · Question 11 · Fundamentals of data representation
The ASCII value for the character x is the decimal number 120. Complete Table 1 with the missing ASCII and Unicode values.
How to approach this question
1. **Understand ASCII:** ASCII values for lowercase letters are sequential. If 'x' is 120, then 'w' (the letter before) must be 119, 'y' must be 121, and 'z' must be 122.
2. **Understand Unicode:** Unicode was designed to be backward-compatible with ASCII. This means that for the first 128 characters (including all the standard English letters, numbers, and symbols), the Unicode value is identical to the ASCII value.
3. **Fill the table:**
* For 'w', the ASCII value is 119. The Unicode value is also 119.
* For 'x', the Unicode value is the same as its ASCII value, 120.
* For 'y', the ASCII value is 121. The Unicode value is also 121.
* For 'z', the ASCII value is 122. The Unicode value is also 122.
Full Answer
This question tests knowledge of character encoding, specifically ASCII and Unicode.
**ASCII (American Standard Code for Information Interchange):** This is a 7-bit character set (often stored in 8 bits/1 byte) that assigns numerical values to letters, numbers, and symbols. The codes for the lowercase alphabet are consecutive. Given that 'x' is 120:
- 'w' is one letter before 'x', so its value is 120 - 1 = 119.
- 'y' is one letter after 'x', so its value is 120 + 1 = 121.
- 'z' is two letters after 'x', so its value is 120 + 2 = 122.
**Unicode:** This is a much larger character encoding standard designed to represent characters from almost all of the world's writing systems. A key feature of Unicode is that its first 128 code points are identical to the ASCII character set for backward compatibility. Since 'w', 'x', 'y', and 'z' are all part of the original ASCII set, their Unicode values are exactly the same as their ASCII values.
Common mistakes
✗ Not knowing that ASCII values for letters are sequential.
✗ Not knowing that Unicode is backward-compatible with ASCII for these characters.
✗ Making simple arithmetic errors.
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