Gigabytes, Terabytes and Petabytes explained

If you are new to computers (or even if you are not), the names applied to different memory sizes may seem strange.

Whether you’re talking about an 8 megabyte memory card, a 500 gigabyte hard drive, or a 1 terabyte SSD, the terms always seem abstract and arbitrary.

How exactly do you measure how much space a gigabyte, a terabyte, or even a petabyte describes?

What is a byte?

To understand how the larger blocks of memory work, it’s important to build an appreciation for the smaller space blocks that make up those larger ones.

In simple terms, a single byte usually consists of eight binary digits. A binary digit is either a 1 or a 0, which in very old computers literally represented a switch that was on or off.

There are some computer systems that have bytes of different lengths, but most modern computers today are based on a binary system of eight bits of bytes.

Those eight bits (a byte) usually represent a character such as a letter or number. Bytes can also represent symbols that represent part of a larger object, such as an image.

Since a “byte” is the smallest data unit, different names are needed for larger data units consisting of even more bits. The most important thing to keep in mind is that all larger units are made up of a fixed number of bytes, and each byte typically contains eight bits.

As you stack more bytes, you can determine the unit name based on the number of bytes.

A kilobyte is 1,024 bytes

You would think that since the prefix “kilo” usually means 1,000, that kilobyte would have 1,000 bytes.

The reality is that since computers store data using the binary system, and the binary system is based on powers of 2, the actual number of bytes is 1,024.

You can see this if you look at how the power of 2’s works.

  • 2^0 = 1
  • 2^1 = 2
  • 2^2 = 4
  • 2^3 = 8
  • 2^4 = 16
  • 2^5 = 32
  • 2^6 = 64
  • 2^7 = 128
  • 2^8 = 256
  • 2^9 = 512
  • 2^10 = 1024

The first binary value representing 1,000 bytes is 1,024. Therefore, a kilobyte contains 1,024 bytes.

You can estimate the size information needs based on the number of characters in that data. Take a 200-page book as an example. Usually, each page in a book has about 300 words per page. That means the entire book is about 60,000 words.

An average word is about 6 characters. That means a book of 60,000 words has about 360,000 characters.

It would take 360,000 bytes to store this book electronically.

You can represent this in kilobytes (KB) by dividing 360,000 bytes by 1024. This means that a 60,000-word book will require approximately 351.56 kilobytes of digital storage space.

What is a gigabyte?

In the metric system, the prefix “Giga” means a unit of measure from 10 to the 9 power, or 1,000,000,000. But remember that to represent this in the computer’s binary system, it has to take into account the binary factor of 2’s.

So, working to Gigabyte with a power of 2, we have to go all the way to 2^30 to get the first number above 1 billion, which is 1,073,741,824 bytes.

Until now you know that a kilobyte is 1024 bytes. What about everything between 1,024 and 1,073,741,824?

  • Kilobyte (KB): One thousand bytes, or one kilobyte, is 1,024 bytes.
  • Megabyte (MB): One million bytes, or one megabyte, is represented as 1,024 kilobytes.
  • Gigabyte (GB): One billion bytes, or one gigabyte, is represented as 1,024 megabytes.

To put the size of a gigabyte into perspective, consider that a single gigabyte can hold about 230 songs, or nearly 600 five-megapixel photos. You could even store a standard 1.5 hour movie on 1 gigabyte.

What is a terabyte?

What is the next power of 10 that is greater than a billion? That would be a trillion.

The prefix for a trillion is “tera”. A terabyte is 10 to the power of 12 bytes, represented in binary.

That means 1 terabyte (TB) is 1024 gigabytes. Most modern hard drives store half this amount of data. A terabyte, a trillion bytes, is a lot of information.

In recent years, manufacturers have started to release new computers with a one- or two-terabyte drive. It would be very difficult for any user to fill such a hard drive unless they are producing many hours of high definition video every day.

Remember that a standard floppy disk drive in the 1990s could only contain thousands of bytes. A CD-ROM can contain 700 megabytes and a DVD-ROM can contain 4.7 GB. But today’s hard drives can store trillions of bytes. A 1 terabyte drive can store 217 DVD-ROMs of data. We’ve come a long way.

What is a petabyte?

The next unit of storage to consider is what is known as a petabyte.

The prefix “peta” is the unit of measure for one quadrillion, or 10 to the power of 15.

Since this is 1,000 units of a trillion (tera), one petabyte is equal to 1,024 terabytes. That’s one quadrillion bytes.

You would think that this amount of information could never be used. Today, petabytes of information flow through computer systems and networks, hard as that may be to believe.

But consider the following petabyte-sized modern uses of technology:

  • Google processes more than 24 petabytes of information every day.
  • Cellular phone networks send more than 20 petabytes to and from users every day.
  • The Blue Waters supercomputer has more than 500 petabytes of tape storage.
  • The United States Library of Congress holds more than 7 petabytes of digital data in its archives.
  • World of Warcraft servers require more than 1.5 petabytes of storage space to run the online game.

The size of a petabyte is hard to wrap your head around, but once you consider the above scenarios, it becomes pretty obvious how much data is involved.

A single petabyte can contain more than 10,000 hours of television programming. If you filled an entire four-drawer file cabinet with documents filled with text, you could fit 20 million of those file cabinets into a petabyte.

In fact, you could store every written manuscript created by mankind since the beginning of recorded history in 50 petabytes.

That’s a lot of data.

Understanding Memory Terminology

It is important to understand the units of memory because today it is used everywhere where there is technology. Every time you buy a computer, a mobile phone or a tablet, the specifications are all written in terms of memory storage and how much data the technology can transmit.

If you understand all these terms, you will know how much better one computer is than another. You will understand how much better a 4G mobile network is than a 3G network. You’ll notice how much more you can store on a 1-terabyte memory card as opposed to a 500-megabyte memory card.

As technology advances, it is possible that there will be new units of memory to learn about. But for now, these terms are all you need to know.

And if you made it this far, check out an article we wrote about understand network transfer speeds, which consists of megabits per second, gigabits per second, etc. This will help you understand when your ISP tells you that your download speed is 15 MBps. Enjoying!

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