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Understanding file sizes | Bytes, KB, MB, GB, TB, PB, EB, ZB, YB

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Pre-Requisite: Computer Memory

The memory of a Computer is any physical device that is capable of storing information whether it is large or small and stores it temporarily or permanently. For example, Random Access Memory (RAM), is a type of volatile memory that stores information for a short interval of time, on an integrated circuit used by the Operating System. 

Memory can be either volatile or non-volatile. Volatile memory is a type of memory that loses its contents when the computer or hardware device is switched off. RAM is an example of a volatile memory i.e. why if your computer gets rebooted while working on a program, you lose all the unsaved data. Non-volatile memory is a memory that keeps its contents saved even in the case of power loss. EPROM((Erasable Programmable ROM) is an example of non-volatile memory. 

What is Memory?

Computer Memory is the hardware part of the system which stores data, information, and instructions. It is a device where data is stored, data is processed and instructions required for data processing are also stored. Computer memory stores both types of data that is, input and output.

Types of Computer Memory

Primary Memory

Primary Memory is called as main memory of the System. During computer operations, it stores data, programs, and instructions. It is commonly called Semiconductor Memory or Volatile Memory. Primary Memory is faster than Secondary Memory.

Secondary Memory

Secondary Memory is used to store a heavy amount of data or information. The data or information stored in Secondary Memory is permanent and secondary memory is slower than primary memory, but secondary memory can’t be directly accessible by the CPU.

Cache Memory

Cache Memory is faster memory that helps in fastening the speed of the CPU. Cache Memory is used to store the data that is frequently required by the CPU. Whenever the system gets off, data present in the cache memory gets lost.

Characteristics of Main Memory

  • Semiconductor memories.
  • Faster than secondary memories.
  • A computer cannot run without primary memory.
  • It is the working memory of the computer.
  • Usually volatile memory.
  • Data is lost in case the power is switched off.

Units of Memory

A computer processor is made up of multiple decisive circuits, each one of which may be either OFF or ON. These two states in terms of memory are represented by a 0 or 1. To count higher than 1, such bits (Binary Digits) are suspended together. A group of eight bits is known as a Byte. 1 Byte can represent numbers between zero (00000000) and 255 (11111111), or 28 = 256 distinct positions. Of course, these bytes may also be combined to represent larger numbers. The computer represents all characters and numbers internally in the same fashion. 

In practice, memory is measured in KiloBytes (KB) or MegaBytes (MB). A KiloByte is not exactly, as one might expect, 1000 Bytes. Rather, the correct amount is 210 i.e. 1024 bytes. Similarly, a megabyte is not 10002 i.e. 1,000,000 bytes, but instead 10242 i.e. 1, 048,576 bytes. This is a remarkable difference. By the time we reach a gigabyte (i.e. 10243 bytes), the difference between the base two and base ten amounts is almost 71 MegaByte.

Both computer memory and disk space are measured in these units. But it’s important not to confuse these two. “12800 KB RAM” refers to the amount of main memory the computer provides to its CPU whereas “128 MB disk” symbolizes the amount of space that is available for the storage of files, data, and other types of permanent information. 

Types of Various Units of Memory

  • Bit
  • Nibble
  • Byte
  • Kilo Byte
  • MegaByte
  • Giga Byte
  • Tera Byte
  • Peta Byte
  • Exa Byte
  • Zetta Byte
  • Yotta Byte


In a computer, data is stored in the form of 0s and 1s. We can store each and every data in a computer with the help of 0s and 1s. Each digit, either 0 or 1, is called a Bit. The Bit is the smallest unit of memory. Bit simply refers to the binary digit.


Nibble is just a greater version of Bit. It is a combination of 4 bits of binary digits or half of an Octet. A nibble can be represented by a single hexadecimal digit.


In computer systems, a unit of data that is eight binary digits long is known as a byte. A byte is a unit that computers use to represent a character such as a letter, number, or a typographic symbol (for example, “h”, “7”, or “$”). A byte can also grasp a string of bits that need to be used in some larger units of application processes (e.g., the stream of bits that composes a visual image for a program that represents images or the string of bits that composes the machine code of a computer program). 
A Byte is abbreviated with a big “B” whereas a bit is abbreviated with a small “b”. Computer storage is generally measured in multiples of the byte. For example, a 640 MB hard drive holds a nominal 640 million bytes – or megabytes – of data. Byte multiples are made up of exponents of 2 and are generally expressed as a “rounded-off” decimal number. For example, two megabytes or 2 million bytes are 2,097,152 (decimal) bytes. 

The Conflict: Once a KiloByte was considered truly massive at a time. Some felt that writing 210 was a bit unwise and also confuse others. 1,024 bytes appeared to be slightly awkward, and for ease of use, the kilobyte began to be referred to simply as 1,000 bytes of data and just ignore the left 24 Bytes. The majority might assume that the KiloByte is just 1, 000 Bytes of data but that’s not the case. This was done as the people with no knowledge of binary will not get the extra 24 bytes of storage.

As time passed, and we started to use MegaByte (MB), it became harder to neglect 24 KB of data, but not hard enough. when GigaByte was started to use it became very hard to ignore 24 MB of storage. Now imagine ignoring 24 GB or even 24 TB of data.

The Solution: Since it was hard to ignore such a large amount of data, they started to call KB 1024 Bytes, 1 GB as 1024 MB, etc. But now it was too late, people now know that the KB was 1, 000 Bytes and not 1, 024 Bytes. An effort was set by the American organization NIST (National Institute of Standards and Time) and the International Electrotechnical Commission (IEC) to resolve the issue. 

As it was very difficult to make small modifications as it tends to big changes to the world of science and technology, it was decided in 1998 that “kibibyte (KiB)” would be used to signify 1,024 bytes while the KiloByte would be retained solely for 1,000 bytes. Similarly “mebibyte (MiB)” would be used to represent 1,048,576 bytes while a megabyte (MB) still referred to 1,000,000 bytes.

Unfortunately, it seems that the actions of these regulators have not helped to clarify the difference between the kilobyte and the kibibyte. The fact that word “kilobyte” has simply become too deep-rooted in international culture.


The kilobyte is the smallest unit of memory measurement but greater than a byte. A kilobyte is 103 or 1,000 bytes abbreviated as ‘K’ or ‘KB’. It antecedes the MegaByte, which contains 1,000,000 bytes. One kilobyte is technically 1,000 bytes, therefore, kilobytes are often used synonymously with kibibytes, which contain exactly 1,024 bytes (210). 
Kilobytes are mostly used to measure the size of small files. For example, a simple text document may contain 10 KB of data and therefore it would have a file size of 10 kilobytes. Graphics of small websites are often between 5 KB and 100 KB in size. Individual files typically take up a minimum of four kilobytes of disk space. 

1 KB = 1,024 Bytes


One megabyte is equal to 1,000 KBs and antecedes the gigabyte (GB) unit of memory measurement. A megabyte is 106 or 1,000,000 bytes and is abbreviated as “MB”. 1 MB is technically 1,000, 000 bytes, therefore, megabytes are often used synonymously with mebibytes, which contain exactly 1, 048, 576 bytes (220). 
Megabytes are mostly used to measure the size of large files. For example, a high-resolution JPEG image might range in size from 1-5 megabytes. A 3-minute song saved in a compressed version may be roughly 3MB in size, and the uncompressed version may take up to 30 MB of disk space. Compact Disk’s capacity is measured in megabytes (approx 700 to 800 MB), whereas the capacity of most other forms of media drives, such as hard drives and flash drives, is generally measured in gigabytes or terabytes. 

1 MB = 1024KB = 1,048,576 Bytes


One gigabyte is equal to 1,000 MBs and precedes the terabyte(TB) unit of memory measurement. A gigabyte is 109 or 1,000,000,000 bytes and is abbreviated as “GB”. 1 GB is technically 1,000,000,000 bytes, therefore, gigabytes are used synonymously with gibibytes, which contain exactly 1,073,741,824 bytes (230). 
Gigabytes, are sometimes also abbreviated as “gigs, ” and are often used to measure a storage device’s capacity. e.g., a standard DVD drive can hold 4.7 GB of data. Storage devices that hold 1, 000 GB of data or more are measured in terabytes. 

1 GB = 1024MB = 1,048,576 KB = 1,073,741,824 Bytes


One terabyte is equal to 1,000 GBs and precedes the petabyte(PB) unit of memory measurement. A terabyte is 1012 or 1,000,000,000,000 bytes and is abbreviated as “TB”. 1 TB is technically 1 trillion bytes, therefore, terabytes and tebibytes are used synonymously, which contains exactly 1, 099, 511, 627, 776 bytes (1, 024 GB) (240). 
Mostly the storage capacity of large storage devices is measured in TeraBytes. Around 2007, consumer hard drives reached a capacity of 1 TeraByte. Now, HDDs are measured in Terabytes e.g., a typical internal HDD may hold 2 Terabytes of data whereas some servers and high-end workstations that contain multiple hard drives may even have a total storage capacity of over 10 Terabytes. 

1 TB = 1024 GB = 1,048,576 
MB = 8,388,608 KB = 1,099,511,627,776 Bytes

Peta Byte

One petabyte is equal to 1,000 TBs and precedes the exabyte unit of memory measurement. A petabyte is 1015 or 1,000,000,000,000,000 bytes and is abbreviated as “PB”. A petabyte is lesser in size than a pebibyte, which contains exactly 1, 125, 899, 906, 842, and 624 (250) bytes. 
Most storage devices can hold a maximum of a few TBs, therefore, petabytes are rarely used to measure the memory capacity of a single device. Instead, PetaBytes are used to measure the total data stored in large networks or server farms. For example, Internet Giants like Google and Facebook store more than over 100 PBs of data on their data servers. 

1 PB = 1024 TB = 1,048,576 GB = 1,073,741,824 
MB = 1,099,511,627,776 KB = 1,125,899,906,842,624 Bytes

Exa Byte

One exabyte is equal to 1, 000 PBs and precedes the zettabyte unit of memory measurement. An exabyte is 1018 or 1,000,000,000,000,000,000 bytes and is abbreviated as “EB”. Exabytes are lesser than exbibytes, which contain exactly 1,152,921,504,606,846, and 976 (260) bytes. 
The exabyte unit of memory measurement is so large, that it is not used to measure the capacity of storage devices. Even the data storage capacity of the biggest cloud storage centers is measured in PetaBytes, which is a fraction of 1 EB. Instead, exabytes measure the amount of data over multiple data storage networks or the amount of data that is being transferred over the Internet for a certain amount of time. E.g., several hundred exabytes of data are transferred over the Internet every year. 

1 EB = 1024 PB = 1,048,576 TB = 1,073,741,824 
GB = 1,099,511,627,776 MB = 1,125,899,906,842,624 KB = 
1,152,921,504,606,846,976 Bytes

Zetta Byte

One zettabyte is equal to 1, 000 exabytes or 1021 or 1,000,000,000,000,000,000,000 bytes. A zettabyte is a little bit smaller than a zebibyte contains 1,180,591,620, 717,411,303,424 (270) bytes, and is abbreviated as “ZB”. One zettabyte contains one billion TBs or one sextillion bytes which means it will take one billion one-terabyte hard drives to store one zettabyte of data. Generally, Zettabyte is used to measure large amounts of data and all the data in the world is just a few zettabytes. 

1 ZB = 1024 EB = 1,048,576 PB = 1,073,741,824 \
TB = 1,099,511,627,776 GB = 1,125,899,906,842,624 MB = 
1,152,921,504,606,846,976 KB = 1,180,591,620,717,411,303,424 Bytes

Yotta Byte

One yottabyte is equal to 1,000 zettabytes. It is the largest SI unit of memory measurement. A yottabyte is 1024 ZettaBytes or 1,000,000,000,000,000,000,000,000 bytes and is abbreviated as “YB”. It is a little bit smaller than yobibyte, which contains exactly 1, 208, 925, 819, 614, 629, 174, 706, and 176 bytes (280) bytes. 

1 yottabyte contains one septillion bytes which is the same as one trillion TBs. It is a very large number that humans can evaluate. There is no practical use for such a large measurement unit because all the data in the world is made of just a few zettabytes. 

1 YB = 1024 ZB = 1,048,576 EB = 1,073,741,824
PB = 1,099,511,627,776 TB = 1,125,899,906,842,624 GB = 
1,152,921,504,606,846,976 MB = 1,180,591,620,717,411,303,424 
KB = 1,208,925,819,614,629,174,706,176 Bytes

Some Misconceptions

  • The size of a disk with one KB is 1024 Bytes although it signifies 1,000 Bytes of data. It’s just the old standard everyone remembers.
  • The download speed Kbps is 1,000 Bits per second, not 1,024 Bits per second.

Tabular Representation of Various Memory Sizes 

NameEqual ToSize (In Bytes)
Bit1 Bit1/8
Nibble4 Bits1/2 (rare)
Byte8 Bits1
Kilobyte1024 Bytes1024
Megabyte1, 024 Kilobytes1, 048, 576
Gigabyte1, 024 Megabytes1, 073, 741, 824
Terrabyte1, 024 Gigabytes1, 099, 511, 627, 776
Petabyte1, 024 Terabytes1, 125, 899, 906, 842, 624
Exabyte1, 024 Petabytes1, 152, 921, 504, 606, 846, 976
Zettabyte1, 024 Exabytes1, 180, 591, 620, 717, 411, 303, 424
Yottabyte1, 024 Zettabytes1, 208, 925, 819, 614, 629, 174, 706, 176


1. Which is bigger: MB or KB?

MB is bigger than KB.

2. How many Gigabytes are there in 1 TeraByte?

There are 1024 GB in 1 TB.

3. How many Bits are there in a Byte?

There are 8 bits in a Byte.

Last Updated : 24 Apr, 2023
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