Data Storage Capacity – Units
Computers store data as binary digits. To describe how much data can be stored, we use units such as bits, bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes. Understanding these units makes it easier to describe file sizes, compare storage devices, and perform storage-capacity conversions.
Bit, Nibble, and Byte
Bit (b)
A bit (binary digit) is the smallest unit of data. It can have one of two values: 0 or 1. Bits are used to represent binary data in a computer.
Nibble
A nibble is a group of 4 bits. Since each bit can be either 0 or 1, four bits can represent (2^4 = 16) different combinations. These combinations can represent values from 0 to 15.
For example, the binary group 0110 is one nibble. Its value is 6 in decimal.
Byte (B)
A byte is a group of 8 bits. It contains two nibbles and can represent (2^8 = 256) different combinations, corresponding to values from 0 to 255.
Key Idea: 4 bits make 1 nibble, while 8 bits make 1 byte. Therefore, 1 byte contains 2 nibbles.
Larger Units of Storage Capacity
Small units such as bits and bytes are not convenient for describing the capacity of modern storage devices. Larger units are used to represent greater amounts of data.
In the binary-unit convention used in this note, each larger unit is 1,024 times the previous unit.
| Unit | Symbol | Value in bytes | Power of 2 |
|---|---|---|---|
| Byte | B | 1 byte (8 bits) | (2^0) |
| Kilobyte | KB | 1,024 bytes | (2^{10}) |
| Megabyte | MB | 1,024 KB | (2^{20}) |
| Gigabyte | GB | 1,024 MB | (2^{30}) |
| Terabyte | TB | 1,024 GB | (2^{40}) |
| Petabyte | PB | 1,024 TB | (2^{50}) |
The relationships can be written as:
- 1 KB = 1,024 bytes
- 1 MB = 1,024 KB
- 1 GB = 1,024 MB
- 1 TB = 1,024 GB
- 1 PB = 1,024 TB
The power-of-two form helps explain the binary relationship. For example, 1 KB is (2^{10}) bytes, and 1 MB is (2^{20}) bytes.
Note: This article follows the 1,024-based convention shown in the supplied note. In some technical contexts, the terms kibibyte (KiB), mebibyte (MiB), and so on are used specifically for powers of 1,024, while kilobyte (kB) and related decimal units may mean powers of 1,000.
Relationships Between Units
To convert between adjacent units:
- Multiply by 1,024 when converting from a larger unit to the next smaller unit.
- Divide by 1,024 when converting from a smaller unit to the next larger unit.
For example, gigabytes are larger than megabytes. Therefore, convert GB to MB by multiplying by 1,024. To convert MB to GB, divide by 1,024.
When converting across more than one unit, apply the conversion factor for each step. For instance, converting TB to bytes requires converting TB to GB, then GB to MB, and then MB to KB and bytes—or multiplying by the corresponding power of 1,024.
Worked Examples: Converting Storage Units
Example 1: Convert 5 KB to bytesSince 1 KB = 1,024 bytes:
(5 \times 1,024 = 5,120) bytes
Therefore, 5 KB = 5,120 bytes.
Example 2: Convert 3 GB to MBSince 1 GB = 1,024 MB:
(3 \times 1,024 = 3,072) MB
Therefore, 3 GB = 3,072 MB.
Example 3: Convert 2 TB to GBSince 1 TB = 1,024 GB:
(2 \times 1,024 = 2,048) GB
Therefore, 2 TB = 2,048 GB.
Understanding File Sizes
File sizes can vary considerably depending on the type of data and how it is stored. The supplied note gives these approximate examples:
| Type of data | Approximate size |
|---|---|
| One-page text document | 20 KB |
| Phone photograph | 2 MB |
| MP3 song | 5 MB |
| One-minute short video | 50 MB |
| Full HD movie | 2 GB |
| Large collection of photographs | 1 TB |
These are illustrative values, not fixed file sizes. Actual sizes depend on factors such as image resolution, audio or video quality, file format, and compression.
The examples show why it is useful to choose an appropriate unit. A small text document can be described in KB, while a movie is more conveniently described in GB.
Storage Capacity and Storage Devices
Storage capacity is the amount of data a storage device can hold. It is not the same as the speed at which the device reads or writes data.
Storage devices can have different capacities. For example, a hard disk, solid-state drive (SSD), pen drive, and memory card may be available in different sizes. When choosing a device, consider how much data needs to be stored as well as other requirements such as speed and portability.
Exam-Focused Points
Key Idea: A bit is the smallest unit of data and can be 0 or 1. A nibble contains 4 bits, and a byte contains 8 bits.
Key Idea: In the 1,024-based system shown here, each larger storage unit is 1,024 times the previous unit.
- 1 byte = 8 bits.
- 1 nibble = 4 bits.
- 1 byte = 2 nibbles.
- 1 KB = 1,024 bytes.
- 1 MB = 1,024 KB.
- 1 GB = 1,024 MB.
- 1 TB = 1,024 GB.
- 1 PB = 1,024 TB.
- Multiply by 1,024 to convert to the next smaller unit; divide by 1,024 to convert to the next larger unit.
- Storage capacity describes how much data can be stored, not the device's speed.
Summary
Data is represented using bits, which can be 0 or 1. Four bits form a nibble, and eight bits form a byte. Larger storage units—KB, MB, GB, TB, and PB—are used to express increasingly large amounts of data. Using the 1,024-based relationships, storage units can be converted by multiplying or dividing by 1,024. These units help describe file sizes and the capacity of storage devices.