What is a byte, and why does it contain 8 bits?

At the most basic level, a byte is a collection of eight bits, or a grouping of 8 'light switches' in RAM. In order to represent a character (in the ASCII character set), we need to examine the pattern of 'on' switches (or '1' bits) and 'off' switches (or '0' bits. For example, to represent the ASCII character 'A', we need the eight bit collection of binary digits: 0100 0001. All computers which use ASCII will interpret this grouping of bits as representing the character 'A'.

Originally, only 7 bits were needed to represent a character. This meant that we could only represent 2⁷ = 128 characters. This became the Standard ASCII Character set. The 8th bit was used to help detect transmission errors using a procedure called parity (the 8th bit being a parity bit).

Once the reliability of computers improved, parity checking became less necessary. Rather than dropping the parity bit, it was utilized to expand the ASCII character set to 256 characters (recall that 2⁸ = 256). This became the Extended ASCII Character Set.

So there it is. Historically, a byte has eight bits. This is unlikely to change, since nearly all computer architecture is based on this principal. However, it is incorrect to learn that a byte equals one character. As the new Unicode standard comes to replace ASCII, a character may be made up of two bytes.

1.   How many bits are ther in a byte? Answer: 8
2.   How many bits are used to represent the Standard ASCII character set? Answer: 7
3.   How many bits are used to represent the Extended ASCII character set?
      a. 2           d.    8
      b. 4           e. 10
      c. 6