CIS3355: Business Data Structures
Fall, 2008
 

What was the problem with coding sequences and how was it resolved?

After it was (more or less) agreed upon that character sets would be developed using 7-bits, computer architects began building computers based on groupings of 7-bits and associated a uniques symbol with each of the groupings.

OK. So what's the problem??

The problem is that they all developed their own coding schemes, none of which corresponded to any of the others.

For example, If there were three manufacturers,  their interpretations of what each 7-bit sequence means might be as follows: 

 So??

The computers couldn't communicate with each other (at least not without an interpreter). Additionally, not all the symbols used were the same. Manufacturer 1, for example, might be the only manufacturer to include the character ¢, manufacturer 2 the symbol ©, and manufacturer 3 the symbol £.

Again, so what??
Are you one of those people who thinks that everyone in the world should speak the same language?

Ah, but computers aren't people. Unlike people, who might have a difficult time learning English, or Spanish or Chinese if they weren't raised with that language, for computers to associate the same bit sequence with the same symbol is quite simple: It is a matter of applying the same look-up tables. This was especially true in the early development of computers when there were not thousands of programs which had been developed based on a particular coding scheme.

Additionally, it is especially important for computers to be able to readily communicate with each other so that they could share data (i.e., as we know from databases, duplicating data can cause a myriad of problems).

Suppose for example, that each post office were allowed to develop their own zipcodes.

How could you ever send a letter to someone outside your zipcode?

 How was the problem solved??

The American Standards Association (ASA), as it was called at that time (now ANSI: The American National Standards Institute), a federal organization intended to coordinate national standards development in an effort to avoid duplication, waste and conflict, devised a coding scheme called ASCII: The American Standard Code for Information Interchange. It became a standard in 1963. Although it has gone through a few revisions since then, it remains the standard used by most computer manufacturers.

 What does the coding scheme look like??

Here are some sample symbols and the binary sequence they correspond to:

And there are 128 7-bit sequences, Right??

Yes and no. The Standard ASCII Character Set still consists of 128 characters (based on 7-bits, obviously, since 2⁷ = 128). However, over time, as errors became less of an issue, all 8-bits in a byte were associated with a unique symbol. Using all 8-bits allows us to represent 256 (Since 2⁸ = 256) symbols (an additional 128 characters). The additional symbols are included in the Extended ASCII Character Set.

Here are some sample symbols and the binary sequence they correspond to in the Extended ASCII Character set:

As you can see it contains a variety of characters from the Greco-Roman Alphabet, as well as a variety of graphical symbols. I have provided you with a complete ASCII table (standard and extended) in the Supplementary Information Page. The tables are also easy to find on-line.

So, Everyone uses ASCII now, right??

Well, no, but we'll discuss that soon. Right after we talk about ASCII Files.

Some good references include:

1. ASCII Definition (Webopedia)

2. A history of ASCII

3. A tutorial on character code issues

At this point in time, you should be able to Answer the following questions:

1. Why was ASCII developed?
   
   Early computers developed their own coding schemes. The problem was that there was not a standardized set of symbols used and symbols which were used in common were not associated with the same bit sequences.
    
2. Why is it important that computers use the same coding scheme?
   
   Computers need to be able to communicate with each other so that they can share information.
    
3. Who developed ASCII and why?
   
   The American Standards Association (ASA), as it was called at that time (now ANSI: The American National Standards Institute), a federal organization intended to coordinate national standards development in an effort to avoid duplication, waste and conflict.
    
4. How many characters are there in the ASCII character set?
   
   The Standard ASCII Character set contains 128 symbols, and the Extended ASCII Character set contains 256 symbols (since it uses all 8-bits)
    

5. What are the ASCII bit sequences used for the following characters:

   a.   NULL                                     g.   0 (zero)
   b.   BEL                                        h.   7
   c.   BackSpace                            i.   A
   d.   CR                                          j.    M
   e.   ESC                                       k.   a
   f.    Space

   Look them up in ASCII table (standard and extended) provided in the Supplementary Information Page.
    
6. ASCII was developed because:
   
   a.   Computer Architects wanted to represent different symbols
   b.   Computer Architects used different bit sequences to represent the same symbols
   c.   Computer Architects needed to standardize the use of parity bits
   d.   A and B
   e.   A and C
   
   Answer: d
    
7. The intent of The American National Standards Institute, the developers of ASCII, was to:
   
   a.   Coordinate National Standards
   b.   Avoid Duplication
   c.   Avoid Waste
   d.   None of the above
   e.   All of the above
   
   Answer: e
    
8. Computers need to be able to communicate with each other in order to:
   
   a.   Share data
   b.   Avoid Duplication
   c.   Avoid Waste
   d.   None of the above
   e.   All of the above
   
   Answer: a
    
9. All of the following symbols/representations are found in the standard ASCII character set except:
   
   a.   NULL
   b.   $
   c.   ESC
   d.   10
   e.   BS
   
   Answer: d
    
10. The standard ASCII Character set consists of how many symbols??
    
    a.   64
    b.   128
    c.   256
    d.   1024
    e.   65,536
    
    Answer: b
     

This page was last updated on 01/08/05