Bytes
Bits are rarely seen alone in computers. They are almost always bundled together into 8-bit collections, and these collections are called bytes. Why are there 8 bits in a byte? A similar question is, "Why are there 12 eggs in a dozen?" The 8-bit byte is something that people settled on through trial and error over the past 50 years.

With 8 bits in a byte, you can represent 256 values ranging from 0 to 255, as shown here:

  0 = 00000000
  1 = 00000001
  2 = 00000010
   ...
254 = 11111110
255 = 11111111
In the article How CDs Work, you learn that a CD uses 2 bytes, or 16 bits, per sample. That gives each sample a range from 0 to 65,535, like this:
    0 = 0000000000000000
    1 = 0000000000000001
    2 = 0000000000000010
     ...
65534 = 1111111111111110
65535 = 1111111111111111

Bytes are frequently used to hold individual characters in a text document. In the ASCII character set, each binary value between 0 and 127 is given a specific character. Most computers extend the ASCII character set to use the full range of 256 characters available in a byte. The upper 128 characters handle special things like accented characters from common foreign languages.

You can see the 127 standard ASCII codes below. Computers store text documents, both on disk and in memory, using these codes. For example, if you use Notepad in Windows 95/98 to create a text file containing the words, "Four score and seven years ago," Notepad would use 1 byte of memory per character (including 1 byte for each space character between the words -- ASCII character 32). When Notepad stores the sentence in a file on disk, the file will also contain 1 byte per character and per space.

Try this experiment: Open up a new file in Notepad and insert the sentence, "Four score and seven years ago" in it. Save the file to disk under the name getty.txt. Then use the explorer and look at the size of the file. You will find that the file has a size of 30 bytes on disk: 1 byte for each character. If you add another word to the end of the sentence and re-save it, the file size will jump to the appropriate number of bytes. Each character consumes a byte.

If you were to look at the file as a computer looks at it, you would find that each byte contains not a letter but a number -- the number is the ASCII code corresponding to the character (see below). So on disk, the numbers for the file look like this:

     F   o   u   r     a   n   d      s   e   v   e   n 
    70 111 117 114 32 97 110 100 32 115 101 118 101 110 
    
By looking in the ASCII table, you can see a one-to-one correspondence between each character and the ASCII code used. Note the use of 32 for a space -- 32 is the ASCII code for a space. We could expand these decimal numbers out to binary numbers (so 32 = 00100000) if we wanted to be technically correct -- that is how the computer really deals with things.

Standard ASCII Character Set
The first 32 values (0 through 31) are codes for things like carriage return and line feed. The space character is the 33rd value, followed by punctuation, digits, uppercase characters and lowercase characters.

      0   NUL
      1   SOH
      2   STX
      3   ETX
      4   EOT
      5   ENQ
      6   ACK
      7   BEL
      8   BS
      9   TAB
     10   LF
     11   VT
     12   FF
     13   CR
     14   SO
     15   SI
     16   DLE
     17   DC1
     18   DC2
     19   DC3
     20   DC4
     21   NAK
     22   SYN
     23   ETB
     24   CAN
     25   EM
     26   SUB
     27   ESC
     28   FS
     29   GS
     30   RS
     31   US
     32
     33   !
     34   "
     35   #
     36   $
     37   %
     38   &
     39   '
     40   (
     41   )
     42   *
     43   +
     44   ,
     45   -
     46   .
     47   /
     48   0
     49   1
     50   2
     51   3
     52   4
     53   5
     54   6
     55   7
     56   8
     57   9
     58   :
     59   ;
     60   <
     61   =
     62   >
     63   ?
     64   @
     65   A
     66   B
     67   C
     68   D
     69   E
     70   F
     71   G
     72   H
     73   I
     74   J
     75   K
     76   L
     77   M
     78   N
     79   O
     80   P
     81   Q
     82   R
     83   S
     84   T
     85   U
     86   V
     87   W
     88   X
     89   Y
     90   Z
     91   [
     92   \
     93   ]
     94   ^
     95   _
     96   `
     97   a
     98   b
     99   c
    100   d
    101   e
    102   f
    103   g
    104   h
    105   i
    106   j
    107   k
    108   l
    109   m
    110   n
    111   o
    112   p
    113   q
    114   r
    115   s
    116   t
    117   u
    118   v
    119   w
    120   x
    121   y
    122   z
    123   {
    124   |
    125   }
    126   ~
    127   DEL