Memory Sizes: Gigabytes, Terabytes, and Petabytes Explained

If you’re new to computers (or even if you’re not), thenames that get applied to different memory sizes can seem strange.

Whether you’re talking about an 8-megabyte memory card, a 500-gigabytehard drive, or a 1 terabyte SSD drive, the terms always seem abstract andrandom.

How exactly do you gauge just how much space a gigabyte, aterabyte, or even a petabyte describes?

What Is a Byte?

To understand how the larger blocks of memory work, it’simportant to build an appreciation for the smaller blocks of space that thoselarger ones are made from.

In simple terms, a single byte is typically eight binarydigits. A binary digit is a 1 or a 0, which in very old computers literallyrepresented a switch that was on or off.

There are some computer systems that have bytes of otherlengths, but most modern computers today are based on an eight-bit byte binarysystem.

Those eight bits (a byte) usually represent a character likea letter or number. Bytes can also represent symbols that represent one pieceof a larger object like an image.

Since a “byte” is the smallest unit of data, then othernames are needed for larger units of data made up of even more bits. The importantthing to keep in mind is that all the larger units are made up of a fixednumber of bytes, and each byte typically contains eight bits.

As you start stacking up more bytes, you can determine thename of the unit based on the number of bytes.

A Kilobyte is 1,024 Bytes

You would think that since the prefix “kilo” typically means1,000, that kilobyte would have 1,000 bytes.

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

You can see this when you look at how the power of 2’sworks.

  • 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 that represents 1,000 bytes is 1,024.Therefore, a kilobyte contains 1,024 bytes.

You can estimate the size that information would requirebased on the number of characters in that data. Take a 200-page book as anexample. Typically, each page in a book has about 300 word per page. That meansthe entire book is about 60,000 words.

An average word is about 6 characters. That means a 60,000-wordbook has about 360,000 characters.

To store this book electronically would require 360,000bytes.

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

What is a Gigabyte?

In the metric system, the prefix “Giga” means a unit ofmeasure of 10 to the power of 9, or 1,000,000,000. But remember, to representthis in the computer binary system, it needs to take the binary factor of 2’sinto account.

So, working up to Gigabyte using power of 2’s, we’ll need to go all the way to 2^30 to get the first number over 1 billion, which is 1,073,741,824 bytes.

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

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

To put the size of a gigabyte into perspective, considerthat a single gigabyte can store about 230 music tracks, or almost 600five-megapixel photographs. You could even store a standard 1.5-hour movie on 1gigabyte.

What Is a Terabyte?

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

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

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

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

Consider that a standard floppy drive in the 1990’s couldhold only thousands of bytes. A CD-ROM could store 700 megabytes, and a DVD-ROMcould store 4.7 GB. But the hard drives of today can store trillions of bytes.A 1 terabyte drive could store 217 DVD-ROM’s worth of data. We’ve come a longway.

What Is a Petabyte?

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

The prefix “peta” is the measurement unit for onequadrillion, or 10 to the power of 15.

Since this is 1,000 units of one trillion (tera), then onepetabyte is equivalent to 1,024 terabytes. That’s one quadrillion bytes.

You would think this volume of information could never beused. However, there are petabytes of information flowing through computersystems and networks today, however hard that may be to believe.

But consider the following modern applications of petabytesized technology:

  • Google processes over 24 petabytes ofinformation every day.
  • Mobile phone networks transmit over 20 petabytesto and from users every day.
  • The Blue Waters supercomputer has over 500petabytes of tape storage.
  • The United States Library of Congress containsover 7 petabytes of digital data in its archives.
  • World of Warcraft servers require over 1.5petabytes of storage to run its online game.

The scale of a petabyte is hard to wrap your head around,but once you consider the scenarios above, it becomes quite clear just how muchdata is involved.

A single petabyte could store over 10,000 hours oftelevision programming. If you filled an entire four-drawer filing cabinet withdocuments filled with text, you could fit 20 million of those file cabinetsinto a petabyte.

In fact, you could store every single written manuscriptcreated by humanity since the beginning of recorded history in 50 petabytes.

That’s a lot of data.

Understanding Memory Terminology

It’s important to understand the units of memory becauseit’s used everywhere where there’s technology these days. Any time you buy acomputer, a mobile phone, or a tablet, the specifications are all written interms of memory storage, and how much data the technology can transmit.

If you understand all these terms, then you’ll know just howmuch better one computer is than other. You’ll appreciate how much better a 4Gmobile network is than a 3G one. You’ll appreciate how much more you’ll be ableto store on a 1 terabyte memory card rather than a 500 megabyte one.

As technology continues to advance, it’s possible there will be new units of memory to learn about. But for now, these terms are all you’ll need to know.

And if you’ve gotten this far, you should jump over to an article we’ve written about understanding 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. Enjoy!