ASCII Code
The standard code for handling text characters on most modern computers is called ASCII (American Standard Code for Information Interchange). The basic ASCII standard consists of 128 codes representing the English alphabet, punctuation, and certain control characters. Most systems today recognize 256 codes: the original 128, plus an additional 128 codes called the extended character set.
Remember that a byte represents one character of information; four bytes are needed to represent a string of four characters. The following four bytes represent the text string 12AB (using ASCII code):
The following illustrates how the binary language spells the word "binary":
NOTE
It is very important to understand that in computer processing the "space" is a significant character. All items in a code must be set out for the machine to process. Like any other character, the space has a binary value that must be included in the data stream. In computing, the absence or presence of a space is critical and sometimes causes confusion or frustration among new users. Uppercase and lowercase letters also have different values. Some operating systems (for example, UNIX) distinguish between them for commands, while others (for example, MS-DOS) translate the uppercase and lowercase into the same word no matter how it is cased.
The following table is a complete representation of the ASCII character set. Even in present-day computing, laden with multimedia and sophisticated programming, ASCII retains an honored and important position.
| Symbol | Binary 1 Byte | Decimal | Symbol | Binary 1 Byte | Decimal |
|---|---|---|---|---|---|
| 0 | 00110000 | 48 | V | 01010110 | 86 |
| 1 | 00110001 | 49 | W | 01010111 | 87 |
| 2 | 00110010 | 50 | X | 01011000 | 88 |
| 3 | 00110011 | 51 | Y | 01011001 | 89 |
| 4 | 00110100 | 52 | Z | 01011010 | 90 |
| 5 | 00110101 | 53 | A | 01100001 | 97 |
| 6 | 00110110 | 54 | B | 01100010 | 98 |
| 7 | 00110111 | 55 | C | 01100011 | 99 |
| 8 | 00111000 | 56 | D | 01100100 | 100 |
| 9 | 00111001 | 57 | E | 01100101 | 101 |
| A | 01000001 | 65 | F | 01100110 | 102 |
| B | 01000010 | 66 | G | 01100111 | 103 |
| C | 01000011 | 67 | H | 01101000 | 104 |
| D | 01000010 | 68 | I | 0110100 | 105 |
| E | 01000101 | 69 | J | 01101010 | 106 |
| F | 01000110 | 70 | K | 01101011 | 107 |
| G | 01000111 | 71 | L | 01101100 | 108 |
| H | 01001000 | 72 | M | 01101101 | 109 |
| I | 01001001 | 73 | N | 01101110 | 110 |
| J | 01001010 | 74 | O | 01101111 | 111 |
| K | 01001011 | 75 | P | 01110000 | 112 |
| L | 01001100 | 76 | Q | 01110001 | 113 |
| M | 01001101 | 77 | R | 01110010 | 114 |
| N | 01001110 | 78 | S | 01110011 | 115 |
| O | 01001111 | 79 | T | 01110100 | 116 |
| P | 01010000 | 80 | U | 01110101 | 117 |
| Q | 01010001 | 81 | V | 01110110 | 118 |
| R | 01010010 | 82 | W | 01110111 | 119 |
| S | 01010011 | 83 | X | 01111000 | 120 |
| T | 01010100 | 84 | Y | 01111001 | 121 |
| U | 01010101 | 85 | Z | 01111010 | 122 |
NOTE
All letters have a separate ASCII value for uppercase and lowercase. The capital letter "A" is 65, and the lowercase "a" is 97.
Keep in mind that computers are machines, and they do not really perceive numbers as anything other than electrical charges setting a switch on or off. Like binary numbers, electrical charges can exist in only two states-positive or negative. Computers interpret the presence of a charge as one and the absence of a charge as zero. This technology allows a computer to process information.