The **storage units of measure **refer to the measurements used to express the amount of data that can be stored on some storage device. These capacities are expressed in terms of bytes.

A bit is the smallest unit of measurement for computer storage. It can have only the value of “0” or “1”, such as electrical off/on or false/true value.

Because the bits are so small, it is rarely used to work with data. For this reason the bits are linked in groups of eight, to form a byte.

Thus, a byte is the primary unit of measurement for data storage. In this unit of measurement, as many as 256 combinations of 0 and 1 can be stored, with which all characters can be represented with the standard ASCII code.

A lowercase “b” is used as an abbreviation for bits, while an uppercase “B” represents bytes. This is an important distinction, since a byte is 8 times larger than a bit.

[toc]

**Difference Between Number Systems**

A computer processor is made up of multiple circuits, each of which can be on or off. These two states are represented by a 1 or a 0 in terms of storage.

A group of eight bits is known as a byte. 1 byte can assign numbers between 0 (00000000) and 255 (11111111), or 2^8=256 different positions.

A kilobyte is not exactly, as one might think, 1,000 bytes. The correct amount is more like 2^10, or 1,024 bytes, because computers use binary (base 2) mathematics, rather than the decimal (base 10) system.

Similarly, a megabyte is not 1,000^2, or 1,000,000 bytes, but 1,024^2, or 1,048,576 bytes. This is a noticeable difference.

When you get to a gigabyte, which is (1,024^3 bytes), you have that there is more than 70 megabytes of difference between the base ten and base two quantities.

**Numerical system used in hard drives**

Many companies that manufacture hard drives use the decimal system to define amounts of storage space. As a consequence, they define 1KB as a thousand bytes, 1MB they define as a million bytes, and so on for all the others.

Since the computer uses the binary system, there is a discrepancy between the capacity displayed on the hard drive and the capacity that the computer will actually recognize.

For example, a hard drive that says it contains 10GB of storage space, when using the decimal system should be able to store 10,000,000,000 bytes. However, in the binary system 10GB is really 10,737,418,240 bytes.

As a result, the computer instead of recognizing 10GB as reported by the hard drive, will only recognize 9.31GB. This does not mean a malfunction, but a matter of using different number systems.

**List of units of measure**

Below is a table of all the standard units of measurement used for data storage:

**Byte**

It is the unit that computers use to assign a character, such as a digit, letter, or symbol. For example, “5”, “j”, or “+”.

Computer storage is measured in multiples of bytes. For example, a 320 megabyte hard drive contains 320 million bytes of data.

Multiples of bytes are given by exponents of 2 and are expressed “rounded” as a decimal number. For example, 2 megabytes or 2 million bytes in the decimal system is actually 2,097,152 bytes.

**Kilobyte**

A kilobyte is 10^3 or 1,000 bytes and is abbreviated as “KB”. However, it contains exactly 1,024 bytes (2^10).

Kilobytes are mainly used to set the size of small files. For example, if a text document contains 25KB of data, then the file would be 25 kilobytes in size.

**Megabyte**

One megabyte is equal to 1,000KB. It is 10^6 or 1,000,000 bytes and is abbreviated as “MB”. It contains exactly 1,048,576 bytes.

They are mainly used to measure the size of large files. For example, a high-resolution JPEG image can range in size from 1 to 5 megabytes.

A 3 minute song saved uncompressed can take up to 30MB of disk space. The capacity of a compact disc (CD) is 700MB.

**gigabytes**

One gigabyte is equal to 1,000MB. It is 10^9 or 1,000,000,000 bytes and is abbreviated as “GB”. It contains exactly 1,073,741,824 bytes.

Often used to measure the capacity of a storage device. For example, a standard DVD drive can hold 4.7 GB of data.

**terabyte**

A terabyte is equal to 1,000GB. It is 10^12 or 1,000,000,000,000 bytes and is abbreviated as “TB”. It contains exactly 1,099,511,627,776 bytes.

The capacity of the largest storage devices is measured in terabytes. In 2008, hard drives had a capacity of 1 terabyte for the first time.

Currently, a typical hard drive can hold 1 terabyte of data, while some high-end servers containing multiple hard drives can have a total storage capacity of more than 12 terabytes.

**petabytes**

A petabyte is equal to 1,000TB. It is 10^15 or 1,000,000,000,000,000 bytes and is abbreviated as “PB”. It contains exactly 1,125,899,906,842,624 (2^50) bytes.

The vast majority of storage devices can contain at most a few TB. For this reason, the petabyte is of no use in establishing the capacity of a single storage device.

Instead, it is used to measure the total amount of data stored in large networks of servers. For example, giants like Google and Facebook store more than 100PB of data on their servers.

**exabyte**

An exabyte is equal to 1,000PB. It is 10^18 or 1,000,000,000,000,000,000 bytes and is abbreviated as “EB”. Contains exactly 1,152,921,504,606,846,976 (2^60) bytes.

This unit of measurement is so large that it is not used to measure the capacity of storage devices.

Instead, it measures the amount of data on multiple data storage networks or the amount of data that is transferred over the Internet during a certain period of time.

**zettabyte**

A zettabyte is equal to 1,000EB. It is 10^21 or 1,000,000,000,000,000,000,000 bytes. It actually contains 1,180,591,620,717,411,303,424 (2^70) bytes and is abbreviated as “ZB”.

It would take a billion 1 terabyte hard drives to store one zettabyte of data. In general, it is used to determine huge amounts of data. All the data in the world is a few zettabytes.

**Yottabyte**

One yottabyte is equal to 1,000ZB. It is 10^24 or 1,000,000,000,000,000,000,000,000 bytes and is abbreviated as “YB”. Contains exactly 1,208,925,819,614,629,174,706,176 bytes (2^80) bytes.

It is too large a number to be able to evaluate. There is currently no practical use for this unit of storage measure.

**References**

Techterms (2012). What units of measurement are used for data storage? Taken from: techterms.com. Indiana University (2018). What are bits, bytes, and other units of measure for digital information? Taken from: kb.iu.edu. Geeks for Geeks (2019). Understanding file sizes | Bytes, KB, MB, GB, TB, PB, EB, ZB, YB. Taken from: geeksforgeeks.org. Byte-notes (2019). Storage Units – Bit, Byte, Nibble. Taken from: byte-notes.com. Casey Schmidt (2019). A Comprehensive Guide to Understanding Digital Storage Units. Singing. Taken from: canto.com.