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A binary digit, or bit, is the smallest unit of information in a computer. It is used for storing information and has a value of true/false, or on/off. An individual bit has a value of either 0 or 1, which is generally used to store data and implement instructions in groups of bytes. A computer is often classified by the number of bits it can process at one time or by the number of bits in a memory address. Many systems use four eight-bit bytes to form a 32-bit word.

The value of a bit is typically stored above or below an allocated level of an electrical charge within a capacitor inside a memory module. For devices that use positive logic, value 1 (true value or high) is positive voltage relative to the electrical ground and value 0 (false value or low) is 0 voltage.

The values 0 and 1 also may be inferred as logical values, like yes/no or true/false, or activation states, such as on/off.

The two values can represent two stable states, such as:

- Voltage/Current: Two distinct levels allowed by a circuit
- Electrical Position: Two positions in which On=1 and Off=0
- Flip-Flop: Used to store information that continually changes between 0 and 1

The technology of reading and storing only two states is referred to as binary technology. The number system that uses the two states is the binary number system. The binary number system does all the counting and calculations in a computer. All numbers and letters are also changed into binary code before being stored in a computer.

For example, counting from zero to 10 in binary looks like this: 0, 1, 10, 11, 100, 101, 110, 111, 1000, 1001, 1010

There is also binary code for uppercase and lowercase letters:

- A: 01000001 a: 01100001
- B: 01000010 b: 01100010
- C: 01000011 c: 01100011

Storing a single character requires eight bits. One byte or eight bits can produce 256 distinctive combinations of numbers, letters, symbols and characters. It takes four eight-bit bytes to form a 32-bit word. The length of a binary number is sometimes referred to as bit length. Many systems use either 32-bit lengths to form a word or 16-bit lengths to form a half-word.

There are many units of information that contain multiples of bits. These include:

- Byte = 8 bits
- Kilobit = 1,000 bits
- Megabit = 1 million bits
- Gigabit = 1 billion bits

Internet connection speeds for downloading and uploading are often referred to as data transfer rates, or bit rates. Bit rate is usually measured in bits per second (bps). Data transfer rates can also be measured in bytes per second (Bps).

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