Consider the following statements about the range of numbers in a 9-bit 1's complement and 2's complement system.
I. In 9-bit 1's complement, the range is -255 to +255, and there exist two representations of zero.
II. In 9-bit 2's complement, the range is -256 to +255, and both 1's complement and 2's complement can represent exactly 512 unique values.
III. The maximum positive number representable is +255 in both 1's complement and 2's complement 9-bit systems.
Identify the CORRECT option.
Explanation
Complete Solution
To evaluate the correctness of each statement, let's use the standard formulas for the range of numbers representable using an n-bit system where n=9.
Analysis of Statement I
Formula for 1's Complement Range:
[−(2n−1−1) to +(2n−1−1)]
Substituting n=9:
Range=[−(29−1−1) to +(29−1−1)]
Range=[−(28−1) to +(28−1)]=[−(256−1) to +(256−1)]=−255 to +255
Representation of Zero: In a 1's complement system, there are two distinct representations for zero: positive zero (+0, represented as 000000000) and negative zero (−0, represented as 111111111).
Conclusion: Statement I is CORRECT.
Analysis of Statement II
Formula for 2's Complement Range:
[−2n−1 to +(2n−1−1)]
Substituting n=9:
Range=[−29−1 to +(29−1−1)]
Range=[−28 to +(28−1)]=−256 to +255
Unique Values Represented:
With 9 bits, there are a total of 29=512 possible binary combinations.
In 2's complement, because there is only one unique representation for zero, all 512 combinations correspond to 512 unique values.
In 1's complement, because zero has two representations (+0 and −0), two different bit patterns represent the exact same value. Therefore, it can only represent 512−1=511 unique values.
Conclusion: Statement II is INCORRECT because 1's complement does not represent 512 unique values.
Analysis of Statement III
Maximum Positive Number in 1's Complement:
+(2n−1−1)=+(28−1)=+255
Maximum Positive Number in 2's Complement:
+(2n−1−1)=+(28−1)=+255
Conclusion: Statement III is CORRECT as both systems share the exact same maximum positive limit for a 9-bit configuration.
Summary Table
Number System (n=9) | Minimum Value | Maximum Value | Total Unique Values | Representations of Zero |
1's Complement | −255 | +255 | 511 | Two (+0 and −0) |
2's Complement | −256 | +255 | 512 | One (0) |
Since only statements I and III are true, the correct choice is option 3.