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1- Bit
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I start the story by talking about base-10 system. When you understand the base-10 system, our story will not be interrupted and confused.
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Okay, the base-10 system is the most popular one but it's not unique. Many cultures used different systems in the past, however, today most of them have moved to base-10 system. The base-10 system uses 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, which are put together to form another number.
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If you only have one box, you can only write a number from 0 to 9. But ..
- If you have two boxes, you can write a number from 0 to 99.
- If you have three boxes, you can write a number from 0 to 999.
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All boxes from right to left have a factor which is in turn 10^0, 10^1, 10^2, ...
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BIT
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BIT is short for
Binary digIT (information unit). A
bit that denotes value 0 or 1, is called the smallest unit in the computer. 0, 1 are two basic digits of base-2 system.
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Let infer as base-10 system and apply it to base-2 system. If you have one box, you can write 2 numbers such as 0 and 1. If you have 2 boxes, you can write 4 numbers such as
00,
01,
10, and
11 (Note: Do not be mistaken, these numbers are ones of base-2 system).
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For base-2 system, the boxes from right to left have 1 factor. They are in turn 2^0, 2^1, 2^2, ...
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The following image describes the way how to convert a number of base-2 system to base-10 system.
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Thus:
- If you have two boxes in the base-2 system, you can write the largest number of 11 (base-2), which is equivalent to 3 in the base-10 system.
- If you have 3 boxes in base-2 system, you can write the largest number of 111 (base-2), which is equivalent to 7 in base -10 system.
And you have the following table:
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| Box Numbers |
Maximum Number (Base-2) |
Convert to Base-10 |
| 1 |
1 |
1 (2^1 - 1) |
| 2 |
11 |
3 (2^2 - 1) |
| 3 |
111 |
7 (2^3 - 1) |
| 4 |
1111 |
15 (2^4 - 1) |
| 5 |
11111 |
31 (2^5 - 1) |
| 6 |
111111 |
63 (2^6 - 1) |
| 7 |
1111111 |
127 (2^7 - 1) |
| 8 |
11111111 |
255 (2^8 - 1) |
| 9 |
111111111 |
511 (2^9 - 1) |
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Why does the computer use base-2 system but not base-10 system?
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You surely ask the question "
Why does computer use base-2 system but not base-10 system?". I have asked this question before, like you.
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Computers operate by using millions of electronic switches (transistors), each of which is either on or off (similar to a light switch, but much smaller). The state of the switch (either on or off) can represent binary information, such as yes or no, true or false, 1 or 0. The basic unit of information in a computer is thus the binary digit (BIT). Although computers can represent an incredible variety of information, every representation must finally be reduced to on and off states of a transistor.
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Thus, the answer is that computer does not have many states to store information, therefore, it stores information based on the two states of
ON and
OFF (1 and 0 respectively).
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Your computer hard drive also stores data on the principle of 0, 1. It includes recorders and readers. It has one or more disks, which are coated with a magnetic layer of nickel. Magnetic particles can have south-north direction or north-south direction, which are two states of magnetic particle, and it corresponds to 0 and 1.
- The reader of hard drive can realize the direction of each magnetic particle to convert it into 0 or 1 signals.
- The data to be stored on hard drive is a line of 0 or 1 signals. The recorder of hard drive relies on this signal and changes the direction of each magnetic particle accordingly. This is the principle of data storage of hard drive.
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2- Byte
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Byte is an unit in computer which is equivalent to 8
bits. Thus, a
byte can represent a number in range of
0 to 255.
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Why is 1 byte equal to 8 bit?
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Your question is now
"Why is 1 byte equal to 8 bits but not 10 bits?".
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At the beginning of computer age people have used
baudot as a basic unit, which is equivalent to 5
bits, i.e. it can represent numbers from 0 to 31. If each number represents a character, 32 is enough to use for the uppercase letters such as A, B, ... Z, and a few more characters. It is not enough for all lowercase characters.
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Immediately after, some computers use 6
bits to represent characters and can represent at maximum 64 characters. They are enough to use for A, B, .. Z, a, b.. Z, 0, 1, 2, .. 9 but not enough for other characters such as +,-,*, / and spaces.Thus, 6
bits quickly become to be restricted.
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ASCII defined a
7-bit character set. That was
"good enough" for a lot of uses for a long time, and has formed the basis of most newer character sets as well (
ISO 646,
ISO 8859,
Unicode,
ISO 10646, etc.)
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ASCII sets:
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8-bit, a little bit more than
7-bit which is better. It doesn't cause too large waste. The
8-bit is a collection of numbers between 0 and 255 and it satisfies computer designers. The concept of
byte was born,
1 byte = 8 bits.
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For
8-bit, Designers can define other characters, including special characters in computer.
ANSI code table was born which is inheritance of the
ASCII code table:
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ANSI Sets:
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There are many character sets with a view to encoding characters in different languages. For example, Chinese, Japanese require a lot of characters, in which case people uses 2
bytes or 4
bytes to define a character.
