Character data

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When you use a computer, which design decision part of the computer might be considered the oldest?

Hint: It has to do with how the human uses interacts with the computer.

A knowledge of characters is important in programming.

Programming languages consist of characters.
Text editors accept keystrokes that represent character data or commands.
Text editor macros developed for productivity require a knowledge of character data.

In the beginning of the computer age, there were only a few characters needed.

All upper case
Digits
Blank
Some punctuation
Some control characters

Over time, more and more characters were added while maintaining compatibility with previous decisions.

1 A=65 a=97 2 B=66 b=98 3 C=67 c=99 4 D=68 d=100 5 E=69 e=101 6 F=70 f=102 7 G=71 g=103 8 H=72 h=104 9 I=73 i=105 10 J=74 j=106 11 K=75 k=107 12 L=76 l=108 13 M=77 m=109 14 N=78 n=110 15 O=79 o=111 16 P=80 p=112 17 Q=81 q=113 18 R=82 r=114 19 S=83 s=115 20 T=84 t=116 21 U=85 u=117 22 V=86 v=118 23 W=87 w=119 24 X=88 x=120 25 Y=89 y=121 26 Z=90 z=122

20 = 32 = " " 21 = 33 = "!" 22 = 34 = "\"" 23 = 35 = "#" 24 = 36 = "$" 25 = 37 = "%" 26 = 38 = "&" 27 = 39 = "'" 28 = 40 = "(" 29 = 41 = ")" 2A = 42 = "*" 2B = 43 = "+" 2C = 44 = "," 2D = 45 = "-" 2E = 46 = "." 2F = 47 = "/"

30 = 48 = "0" 31 = 49 = "1" 32 = 50 = "2" 33 = 51 = "3" 34 = 52 = "4" 35 = 53 = "5" 36 = 54 = "6" 37 = 55 = "7" 38 = 56 = "8" 39 = 57 = "9"

3A = 58 = ":" 3B = 59 = ";" 3C = 60 = "<" 3D = 61 = "=" 3E = 62 = ">" 3F = 63 = "?" 40 = 64 = "@"

ASCII uppercase letters start at 41h or 65d

5B = 91 = "[" 5C = 92 = "\\" 5D = 93 = "]" 5E = 94 = "^" 5F = 95 = "_" 60 = 96 = "`"

ASCII uppercase letters start at 61h or 97d

7B = 123 = "{" 7C = 124 = "|" 7D = 125 = "}" 7E = 126 = "~"

ASCII character 127d or 7Fh is the delete character, a control character.

127d = 7Fh = 01111111b

It is also known as the rubout character since, on a paper take, all the holes could be punched to ignore that character.

On the IBM PC and thereafter, the backspace character, Ctrl-H, 08d = 08h = 00001000b, was used for deleting the previous character

With the introduction of the IBM PC in 1981, extended ASCII was introduced.

This provided characters in the range 128d to 255d, 80h to FFh, 10000000 b to 1111 111 b.

Problem: Many vendors provided different characters in this range.

Solution: Code page switching - still causing issues today.

Signature pattern: ASII characters are recognized and displayed properly but not the extended ASCII.

The Unicode-2 (2 bytes) or Unicode-16 (16 bites) (same format) character representation format allows 65535 characters to be represented.

The UTF-8 encoding is the most popular encoding since most characters are in the 0 to 127 range.

Unicode allows more characters to be represented (e.g., for ancient fonts such as Gothic) but many times the software being used does not properly support such representations.

The leading bits serve as a state machine for what to expect next.
There is some fault tolerance so that the sequence/state can be picked up after an error.

1 byte : 0-127: 7 bits 0 x x x x x x x : 7 bits : 0-127

2 bytes: 128-2047: 5 + 6 = 11 bits 1 1 0 x x x x x : 5 bits : 0-31 : 110xxxxx = 192-223 1 0 x x x x x x : 6 bits: 0-63 : 10xxxxxx = 128-191

3 bytes : 2048-65,535: 4 + 6 + 6 = 16 bits 1 1 1 0 x x x x : 4 bits : 0-15 : 1110xxxx = 224-239 1 0 x x x x x x : 6 bits: 0-63 : 10xxxxxx = 128-191 1 0 x x x x x x : 6 bits: 0-63 : 10xxxxxx = 128-191

4 bytes : 65,536-1,114,111: 3 + 6 + 6 + 6 = 21 bits 1 1 1 1 x x x x : 3 bits : 0-15 : 1111xxxx = 240-255 1 0 x x x x x x : 6 bits: 0-63 : 10xxxxxx = 128-191 1 0 x x x x x x : 6 bits: 0-63 : 10xxxxxx = 128-191 1 0 x x x x x x : 6 bits: 0-63 : 10xxxxxx = 128-191