Byte

   Byte (symbol: B) is a basic unit of [1]information, nowadays already
   practically always consisting of 8 [2]bits (for which it's also called an
   octet), that allow it to store 2^8 = 256 distinct values (for example a
   number in range 0 to 255). It is commonly the smallest unit of computer
   memory a [3]CPU is able to operate on; memory addresses are assigned by
   steps of one byte. We use bytes to measure the size of [4]memory and
   derive higher memory [5]units such as a kilobyte (kB, 1000 bytes),
   kibibyte (KiB, 1024 bytes), megabyte (MB, 10^6 bytes) and so forth. In
   conventional [6]programming a one byte [7]variable is seen as very small
   and used if we are really limited by memory constraints (e.g. [8]embedded)
   or to mimic older 8bit computers ("[9]retro games" etc.): one byte can be
   used to store very small numbers (while in mainstream processors numbers
   nowadays mostly have 4 or 8 bytes), text characters ([10]ASCII, ...), very
   primitive [11]colors (see [12]RGB332, [13]palettes, ...) etc.

   Historically byte was used to stand for the basic addressable unit of
   memory capable of storing one text character or another "basic value" and
   could therefore have a different size than 8 bits: for example ASCII
   machines might have had a 7bit byte, 16bit machines a 16bit byte etc.; in
   [14]C (standard 99) char is the "byte" data type, its byte size is always
   1 (sizeof(char) == 1), though its number of bits (CHAR_BIT) can be greater
   or equal to 8; if you need an exact 8bit byte use types such as int8_t and
   uint8_t from the standard stdint library. From now on we will implicitly
   talk about 8bit bytes.

   Value of one byte can be written exactly with two [15]hexadecimal digits
   with each digit always corresponding to higher/lower 4 bits, making mental
   conversions very easy; this is very convenient compared to [16]decimal
   representation, so programmers prefer to write byte values in hexadecimal.
   For example a byte whose binary value is 11010010 is D2 in hexadecimal
   (1101 is always D and 0010 is always 2), while in decimal we get 210.

   Byte frequency/probability: it may be [17]interesting and/or useful (e.g.
   for [18]compression) to know how often different byte values appear in the
   data we process with computers -- indeed, this always DEPENDS; if we are
   working with plain [19]ASCII text, we will never encounter values above
   127, and on the other hand if we are processing photos from a polar
   expedition, we will likely mostly encounter byte values of 255 (as snow
   will cause most pixels to be completely white). In general we may expect
   values such as [20]0, 255, [21]1 and [22]2 to be most frequent, as many
   times these are e.g. assigned special meanings in data encodings, they may
   be cutoff values etc. Here is a table of measured byte frequencies in real
   data:

   { Measured by me. ~drummyfish }

   type of data      least c.  2nd least 3rd least 3rd     2nd most most c.   
                               c.        c.        most c. c.       
   GNU/Linux x86     0x9e (0%) 0xb2 (0%) 0x9a (0%) 0x48    0xff     0x00      
   executable                                      (2%)    (3%)     (32%)     
   bare metal ARM    0xcf (0%) 0xb7 (0%) 0xa7 (0%) 0xff    0x01     0x00      
   executable                                      (2%)    (3%)     (15%)     
   UTF8 English txt  0x00 (0%) 0x01 (0%) 0x02 (0%) 0x74    0x65 (e, 0x20 (  , 
   book                                            (t, 6%) 8%)      14%)      
   C source code     0x00 (0%) 0x01 (0%) 0x02 (0%) 0x31    0x20 (   0x2c (,,  
                                                   (1, 6%) , 12%)   16%)      
   raw 24bit RGB     0x07 (0%) 0x09 (0%) 0x08 (0%) 0xdd    0x00     0xff      
   photo image                                     (0%)    (1%)     (25%)     

Links:
1. information.md
2. bit.md
3. cpu.md
4. memory.md
5. memory_units.md
6. programming.md
7. variable.md
8. embedded.md
9. retro.md
10. ascii.md
11. color.md
12. rgb332.md
13. palette.md
14. c.md
15. hexadecimal.md
16. decimal.md
17. interesting.md
18. compression.md
19. ascii.md
20. zero.md
21. one.md
22. two.md