For example, 01000001, or decimal equivalent of 65 and hexadecimal equivalent of 41, is the alphabet "A". Note that upper cases and lower cases have distinct representations that differ by 32 decimal or 20 hexadecimal. To enter a character that your PC keyboard does not have, you enter the ASCII number with the number keys in the number key pad section (not the numbers at the top of the keyboard) while pressing down the "ALT" key, When you release the ALT key, the character is entered. For example, ALT-65 gives you an "A". Another example: blank space is ASCII 32 decimal or ASCII 20 hexadecimal; thus, a blank space in a URL is represented as "%20", e.g., "www.nogood.edu/nobody/%20/abc." Below are other ASCII characters represented in the "%" form in a URL. URL does not support special characters, e.g., the graphical characters of the upper half of the ASCII table nor the unicode.
%20 blank
%21 !
%22 "
%23 #
%24 $
%25 %
%26 &
%27 '
%28 (
%29 )
%2A *
%2B +
%2C ,
%2D .
%2E .
%2F /
%30 0
%31 1
%32 2
%33 3
%34 4
%35 5
%36 6
%37 7
%38 8
%39 9
%3A :
%3B ;
%3C <
%3D >
%3E >
%3F ?
%40 @
%41 A
%42 B
%43 C
%44 D
%45 E
%46 F
%47 G
%48 H
%49 I
%4A J
%4B K
%4C L
%4D M
%4E N
%4F O
%50 P
%51 Q
%52 R
%53 S
%54 T
%55 U
%56 V
%57 W
%58 X
%59 Y
%60 `
%61 a
%62 b
%63 c
%64 d
%65 e
%66 f
%67 g
%68 h
%69 i
%6A j
%6B k
%6C l
%6D m
%6E n
%6F o
%70 p
%71 q
%72 r
%73 s
%74 t
%75 u
%76 v
%77 w
%78 x
%79 y
%7A z
%7B {
%7C |
%7D ~
%7E ~
%7F (DEL char)
There are a number of tricks with nonstandard characters. For example, you can create files named with graphical characters. You can create a file with ASCII 255 -- another blank character that does not show up but differs completely from the blank space character of ASCII 32.
------------------------------------------------- CTRL Key Meaning ------------------------------------------------- CTRL-C kill a program CTRL-D eof (end-of-file) character in UNIX CTRL-G bell CTRL-H backspace CTRL-I horizontal tab CTRL-J line feed CTRL-K vertical tab CTRL-L form feed (page eject) CTRL-M carriage return (enter key) CTRL-P toggle display echo to printer CTRL-Q restart a suspended program CTRL-S suspend a program CTRL-Z eof (end-of-file) character in DOS -------------------------------------------------
Side note: With the additional language settings, more recent versions of Windows allow 2-byte based Unicodes, although still not quite seemlessly.
Unfortunately, mainly because of politics, there are several Chinese coding systems. The most common ones are GuoBiao (GB), which is commonly used in mainland China and Singapore; Big5, which is popular in Taiwan and Hong Kong; and the Unicode. GB contains about 6500 Chinese characters, where the first and second bytes are both coded from Hex A1 to Hex FE. On the other hand, Big5 contains about 13000 characters, where the first byte is coded from Hex A1 to FE and the second byte from Hex 40 to 7F or Hex A1 to FE. Note the 127 standard ASCII alphabets are intermeshed with GB and Big5. Furthermore, to make the matter worse, many languages, including Japanese and Korean use a subset or a variant of the Chinese characeters (kanji). Each of these languages, in turn, has several encoding systems. Some people speculate that Unicode, which is adopted in MS IE5, will eventually become the standard, and we we no longer need to worry about the encoding scheme.
Computer Nature
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# Possible States 2 (0 & 1) 4 (A, T, C G)
# of Characters 26+ alphabets 20 amino acids
# of Binary-Quad Digits Needed 8 3
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