wpe41.gif (23084 bytes)CIS3355: Business Data Structures
Fall, 2008
 

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

The simple definition of a byte is that it is a grouping of 8-bits.

What does that mean??

As we already know (See the tutorial on What does a BIT stand for? ), The 'lightswitches' in a computer are grouped together and interpreted according to some agreed upon scheme (Generally, the ASCII coding scheme). (Almost) Any character can be represented using a unique pattern of 'on' switches (or '1' bits) and 'off' switches (or '0' bits).  

For example, to represent the ASCII character 'A' (Uppercase 'a'), we need the eight bit grouping of binary digits:

01000001

As long as we agree that whenever we see this grouping of bits, we interpret the pattern as meaning the Character A, we can communicate with each other.

But, why eight bits??

When early computer engineers were developing their machines, they felt that they needed to represent approximately characters. This meant that they needed 7 bits were needed to represent a character (since 27 = 128 characters.  This became the Standard ASCII Character set.

Again, why eight bits??

The 8th bit was used to help detect transmission errors using a procedure called Parity (the 8th bit being the Parity Bit). (The use of Parity will be discussed in detail later)

Once the reliability of computers improved, parity checking became less necessary (today's transmissions have much more sophisticated techniques for detecting and correcting errors).  That meant that all 8-bits could be utilized, meaning that we could represent 28 or 256 characters.  This became the Extended ASCII Character Set.

Why is it called a byte??

Basically, there had to be a term associated with this grouping. IBM was (by far) the dominating factor in computer design and architecture, and that was the term they came up.

Questions you should be able to answer after reading this tutorial:

1.   How many bits do we need to represent a character?

Answer: That depends on how many characters we wish to represent. Early computer architects decided they needed about 100 characters. Since 6 bits were too few (26 = 64), they decided on 7 bits (since 26 = 64),

2.   If the standard ASCII character set consists of 7 bits, why does a byte consist of 8 bits?

Answer: Initially, an 8th bit was added to help catch transmission errors (A Parity bit).

3.   How many bits are used to represent the Extended ASCII character set?


      a.  2           d.    8
      b.  4           e.  10
      c.  6

      Answer: d

References:

http://www.howstuffworks.com/bytes.htm
http://newbieclub.com/bytes/?byhb

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