The original ASCII character encoding standard used how many bits of each 8 bit byte for the character code, leaving the remaining bit available for parity or error checking?

Introduction / Context:
ASCII, which stands for American Standard Code for Information Interchange, is one of the earliest widely adopted character encoding standards in computing. It specifies numeric codes for letters, digits, punctuation, and control characters. When ASCII was first designed, hardware designers frequently used 8 bit bytes, but not all 8 bits were used for the actual character code. This question asks how many bits in each byte were dedicated to the ASCII character itself, with the remaining bit left for parity or error checking.

Given Data / Assumptions:
- We are dealing with the original ASCII standard, not extended or Unicode encodings.
- Bytes in many systems are 8 bits long.
- The question states that one bit was reserved for parity or error checking.
- The remaining bits in the byte are used to store the ASCII character value.

Concept / Approach:
ASCII was originally defined as a 7 bit code, allowing for 128 distinct characters, from code 0 to code 127. These include control characters such as line feed and carriage return, as well as printable characters like letters and digits. On systems where a byte consists of 8 bits, it was common to use 7 bits for the ASCII code and retain the eighth bit as a parity bit. Parity bits support simple error detection methods in data transmission and storage. Therefore, the correct count of bits used for the ASCII character is 7, not 5, 6, or all 8 bits.

Step-by-Step Solution:
Step 1: Remember that ASCII originally defined 128 characters, which requires 7 bits because 2^7 equals 128. Step 2: Recognise that an 8 bit byte can represent 256 different combinations, but ASCII did not need all of these, so designers chose to use only 7 bits for the character code. Step 3: Understand that the extra bit could be used for parity, a simple error checking technique that counts bits set to one. Step 4: Evaluate each option. Five bits allow only 32 combinations, and six bits allow 64, both too few to cover all ASCII characters. Step 5: Observe that using all 8 bits would allow 256 characters and would not leave a separate parity bit, which contradicts the information in the question. Step 6: Conclude that the character code uses 7 bits of each byte, which matches the standard size of the ASCII code space.

Verification / Alternative check:
Textbooks on computer architecture and data communication describe ASCII as a 7 bit character set. They often show tables with codes from 0 to 127 and explain that extended ASCII versions use the eighth bit to support additional characters. They also discuss parity bits as a common error detection feature in early serial communication protocols. These sources confirm that in classic implementations, ASCII characters occupied 7 bits, with the remaining bit of the 8 bit byte often assigned to parity, exactly as the question describes.

Why Other Options Are Wrong:
5 bits for each character: Five bits can encode only 32 unique values, not enough for the full ASCII set of 128 characters.
6 bits for each character: Six bits permit 64 combinations, still insufficient for ASCII, which needs 128 character codes.
All 8 bits for each character: This contradicts the question statement that one bit is reserved for error checking, and also does not reflect the original 7 bit ASCII design.

Common Pitfalls:
A common error is to assume that because modern computers use 8 bit bytes, all character encodings must also be 8 bit by default. Learners may overlook the historical fact that ASCII was defined as a 7 bit code and that extended ASCII and Unicode came later. Another pitfall is to confuse the capacity of a byte with the actual number of bits used for data in specific protocols. To avoid this confusion, always distinguish between the size of the storage unit and the number of bits that a particular standard chooses to use within that unit.

Final Answer:
The original ASCII standard used 7 bits for each character, leaving the eighth bit of an 8 bit byte available for parity or error checking.