Units of storage in computers: What are digital units of meas­ure­ment?

How much internal storage should a good smart­phone have? How much RAM is re­com­men­ded? How many gigabytes does a terabyte hard drive contain and what are kilobytes and megabytes anyway? We use feet to measure the world’s highest mountains, and bytes to measure the ever-growing mountains of data. If you want to be able to un­der­stand different storage ca­pa­cit­ies and the pro­por­tions of different groups of data, you’ll need to be familiar with the units of storage in computers, starting with the smallest one – the byte – and going all the way up to zetta-, yotta-, and bron­to­bytes.

Few people are aware that we now live in the era of the zettabyte. In 2016, the amount of data generated annually reached the size of one zettabyte. It’s estimated that by the year 2025 there will exist 175 zetta­bytes of data worldwide. How does that translate? One zettabyte contains one billion terabytes. Hard drives that are con­sidered to have large storage capacity have at least one terabyte of memory. One terabyte is enough space for 250 two-hour long HD movies. One zettabyte thus cor­res­ponds to 250,000,000,000 HD films!

Since digital ap­plic­a­tions, smart tech­no­lo­gies, and the Internet itself have become a fixed part of our lives, data quant­it­ies have exploded. Busi­nesses and private in­di­vidu­als produce so much data that it can no longer be clearly expressed in bits and bytes. Every day, about 2.5 quin­til­lion bytes are produced worldwide. Humanity’s digital footprint is thus barely com­pre­hens­ible. However, knowing the storage units for computers goes a long way to helping one un­der­stand how big a set of data actually is.

The smallest unit of in­form­a­tion is a bit. Even the largest mountains of data start there, since a bit is the smallest possible dis­tinc­tion that a computer can make: 1 or 0. In pro­gram­ming, this is called a ‘Boolean’. There’s nothing smaller than a bit – the state 1 or 0 for digital ap­plic­a­tions, and since computers com­mu­nic­ate in binary, data sets are cal­cu­lated in ones and zeros.

Try imagining storage units in computers as con­tain­ers. A bit is the smallest container and holds just one piece of in­form­a­tion. It is not yet a data set, as data sets consist of many con­tain­ers with many pieces of in­form­a­tion.

The word ‘bit’ is an ab­bre­vi­ation for ‘binary in­form­a­tion digit’ and was used for the first time by American math­em­atician John W. Turkey in a Bells Lab memo. The term started being more widely used after Claude E. Shannon used it in his 1948 treatise ‘A Math­em­at­ic­al Theory of Com­mu­nic­a­tion’.

The word ‘byte’ (B) was coined in 1956 by IBM engineer Werner Buchholz to describe a group of bits. Data quant­it­ies and thus also storage units in computers are always given in bytes.

One byte consists of 8 bits and is ab­bre­vi­ated by a ‘B’. Since one bit can convey one of two states (i.e., 1 or 0), a byte can convey 256 (2⁸) different states. That’s because each of the 8 bits in a byte presents 8 chances for a bit to be set to 1:

10000000

01000000

00100000

00010000

00001000

00000100

00000010

00000001

Various prefixes come in handy for dif­fer­en­ti­at­ing among quant­it­ies of data that are larger than just a few bytes: for example, kilobyte, megabyte, and gigabyte. In es­tab­lish­ing these prefixes, the decimal system that humans commonly use and the binary system used by computers come head to head. That’s why there are two systems for labelling data quant­it­ies: binary prefixes and decimal prefixes.

Binary prefixes, also referred to as IEC prefixes, define data quant­it­ies in powers of two (i.e., 2^x). Decimal prefixes, also called SI prefixes, stand for powers of ten (i.e., 10^x).

A computer needs 1 byte to store one character. This gives us the following:

1 byte = 1 character (e.g., A, Z, ?, 5, 0, #)

1 kilobyte cor­res­ponds to 1,024 bytes, or 1,024 different char­ac­ters.

One page of text with 1,800 char­ac­ters including spaces thus cor­res­ponds to about 1,800 bytes or 1-2 kilobytes. In programs like Word, format­ting and graphics can quickly bring that number up to 10-12 KB. But these are still very small units of storage for computers.

In contrast, a smart­phone with a 12-megapixel camera takes photos that are 2-4.5 MG per picture. Com­mer­cially available laptops have 8, 12 or 16 GB in RAM. And hard drives have long been available in the terabyte range.

The following chart might help you un­der­stand the con­ver­sions between storage units:

This next chart provides an overview of how many bytes each data quantity contains when using decimal prefixes for binary units (as is standard practice):

The standard unit for large storage volumes is currently terabytes. External hard drives typically offer 1-5 terabytes of memory. Con­sid­er­ing that 44 trillion gigabytes are produced annually, that’s actually not very much.

The next biggest units of storage in computers are petabytes and exabytes, which are mostly relevant in the everyday business of tech giants like Google and Apple. Google reports that it has a data volume between 10 and 15 exabytes. That amounts to around 30 million computers put together.

Exabytes are followed by zetta­bytes, the unit used to describe the amount of data generated annually. It’s estimated that humanity produced up to 59 zetta­bytes of data in 2020 alone. Zetta­bytes are followed by yot­ta­bytes and this is where things begin to get a bit the­or­et­ic­al. The yottabyte is the biggest storage capacity currently accepted by the In­ter­na­tion­al System of Units. Yot­ta­bytes are mostly relevant in the context of the personal data in­tel­li­gence agencies have stored worldwide - very big data.

But of course, that’s not where it ends. Mass data like bron­to­bytes and gegobytes are such large, purely the­or­et­ic­al quant­it­ies of data that they’re not of­fi­cially re­cog­nized by the In­ter­na­tion­al System of Units. It’s predicted that in 2030, the amount of data generated annually will reach 1 bron­to­byte for the first time. To put it in physical terms: Given the size of today’s hard drives, a one-gegobyte hard drive would be 23,000,000 times larger than the surface area of the earth.

Whereas storage units in terabytes are still com­pre­hens­ible, di­men­sions like 175 zetta­bytes are abstract and near im­possible to grasp. These simple, concrete examples make it a bit clearer:

1 nibble = 4 bits

1 byte = 1 letter/character

1 kilobyte = 1 standard page (1,800 char­ac­ters)

1 megabyte = approx. 1 book with 200 pages

2–5 megabyte = 1 HD movie

1 gigabyte = approx. 1,000–2,000 books

1 terabyte = approx. 250,000 MP3 songs

1 petabyte = approx. 223,000 HD movies or 745 million floppy disks

1 exabyte = approx. 12 billion DVDs or 16 trillion MP3 songs

1 zettabyte = all of the data generated worldwide in 2016

1 yottabyte = approx. 45 quin­til­lion Blu-ray Discs with 25 GB each

According to sci­ent­ists, the storage capacity of the human brain is estimated to be around 2.5 petabytes. That’s 1,024 external hard drives with 1 terabyte storage volume each. Why we still can’t seem to remember our email passwords or friends’ birthdays remains a mystery!