Bits are the fundamental building blocks of digital data. Do you know why a bit (binary digit) is the smallest unit of digital information?
The word binary means two possible states or values. The prefix bi- means “two,” so a binary system is based on two choices.
For example, a quiz might ask whether a statement is true or false. Since there are only two possible answers, this is a binary question. Another common example is a traditional light switch. It can only be in one of two states: on or off. At any given moment, the switch cannot be both on and off or somewhere in between.
In computing and digital electronics, these two states are often represented by the numbers 0 and 1. By convention, 0 usually represents off, false, or the absence of a signal, while 1 represents on, true, or the presence of a signal.
Computers use binary because electronic circuits can reliably detect two electrical states, such as low voltage and high voltage. By combining many 0s and 1s, computers can represent numbers, letters, images, sounds, and software. Although a single binary digit (called a bit) can store only one of two values (0 or 1), groups of bits can represent a vast amount of information.
Bits, Bytes, and Nibbles
More bits means more information that can be represented with the binary system.
In introductory computer science, a byte is a sequence of 8 bits. One byte can represent 256 different possible values (from 0 to 255). Half of a byte is called a nibble. A word is a group of 16, 32, or 64 bits that are processed together. A word of thirty-two bits can represent a value between 0 and 4 billion.
A simplified progression of bit sequences:
- Bit (b): A single binary value that can be either 0 or 1.
- Nibble: 4 bits.
- Byte (B): 8 bits.
- Kilobyte (KB): About 1,000 bytes.
- Megabyte (MB): About 1,000 kilobytes (about 1 million bytes).
- Gigabyte (GB): About 1,000 megabytes (about 1 billion bytes).
- Terabyte (TB): About 1,000 gigabytes (about 1 trillion bytes).
Decimal vs Binary
How many bits are in a terabyte? That may sound like a simple question, but determining how many bits are in a terabyte depends on which definition you use.
Using the decimal (SI) definition, which is the standard used by many drive manufacturers, 1 terabyte (TB) equals 10¹² bytes (1,000,000,000,000 bytes). Since 1 byte = 8 bits, a decimal terabyte contains 8,000,000,000,000 bits (8 trillion bits).
Using the binary definition, the equivalent unit is actually called a tebibyte (TiB), not a terabyte. 1 TiB equals 2⁴⁰ bytes (1,099,511,627,776 bytes). Multiplying by 8 bits per byte gives 8,796,093,022,208 bits.
- 1 KiB = 1,024 bytes
- 1 MiB = 1,024 KiB
- 1 GiB = 1,024 MiB
- 1 TiB = 1,024 GiB
Discussion Questions
Why might a 1TB hard drive appear to have only about 90% capacity?
Hard drive manufacturers typically use the decimal definition. However, operating systems may display storage amounts using binary multiples, but label them as decimal (KB/MB/GB/TB) instead of the more precise binary (KiB/MiB/GiB/TiB). This is why a 1TB hard drive may appear to have only about 0.91 TB of usable capacity in some systems.
The prefix “kilo” refers to 1000, so how did it come to represent 1024 bytes?
The use of “kilobyte” to mean 1,024 bytes is a historical convention that predates the standardized binary prefixes. The metric prefix kilo has always meant 1,000. Early computer engineers borrowed the term kilobyte to mean 1,024 bytes because computers use binary, and 1,024 (2¹⁰) is very close to 1,000 (10³); saying the word kilo was easier than saying 1, 024 bytes. This informal usage became widespread.
Standardized Binary Prefixes
The terms kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), and tebibyte (TiB) were introduced specifically to avoid confusion with decimal SI prefixes (such as kilo).
- kibi Ki 210
- mebi Mi 220
- gibi Gi 230
- tebi Ti 240
- pebi Pi 250
- exbi Ei 260
- zebi Zi 270
- yobi Yi 280
Origin of “Bit”
The word “bit” is a portmanteau of “binary digit”.
A portmanteau merges partial elements of two words. In this case, it can be thought of as blending the “b” of binary and the “its” of digits. (A compound word in comparison keeps full words together, such as “sun” and “flower” to make sunflower.)
Review Questions
- What is the smallest unit of information in a computer?
- Why do computers use binary?
- How many bits are in a terabyte?
- Bonus trivia question: What is half a byte?
- A bit is the smallest unit of information in a computer. It can have one of two possible values: 0 or 1. It can also be described as any combination of two states (such as positive or negative, on or off, true or false, or open and closed).
- Computers use binary because electronic circuits can reliably detect two electrical states, such as low voltage and high voltage.
- There are approximately 8 trillion bits in one terabyte. An exact answer depends on whether you are using a decimal or binary definition.
- 1TB (decimal): 8,000,000,000,000 bits (or 1,000,000,000,000 bytes)
- 1TiB (binary): 8,796,093,022,208 bits (or 1,099,511,627,776 bytes)
- Half of a byte (4 bits) is called a nibble. The name is a play on words: a nibble is a smaller “bite” (byte).
Summary
A bit (binary digit) is the smallest unit of information in a computer. A bit can store one of two possible values: 0 or 1.
When something has exactly two possible states, it can be described as binary. Examples : true or false, yes or no, on or off, open or closed, 0 or 1.
The decimal (SI) definition (used by many drive manufacturers) states that 1 terabyte (TB) equals 1012 bytes. The binary definition says the equivalent unit is a tebibyte (TiB) and it equals 240 bytes.
- Decimal: KB/MB/GB/TB
- Binary: KiB/MiB/GiB/TiB
Expand Your Knowledge
- Binary Numeral System (Base-2)
- Decimal Numeral System (Base-10)
- Hexadecimal Numeral System (Base-16)
- Numeral Systems and Data Representation
- Decimal and Binary: Numeral System Conversions
- IEEE/ASTM Standard for Use of the International System of Units (SI): The Modern Metric System
- The International System of Units (SI), 2019 Edition
