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Memory Sizes Explained – Gigabytes, Terabytes & Petabytes in Layman’s Terms
by Joel Lee It’s easy to see that 500 gigabytes is more than 100 gigabytes. It’s also easy to see that 1 terabyte is larger than 1 gigabyte and that is larger than 1 megabyte. But these are all abstract terms and names. We can visualize 1 inch or 1 meter or 1 mile, but how can we visualize 1 gigabyte? 1 terabyte? 1 petabyte? Our technology has progressed very far in the last decade or so, and with so much memory space available, it’s hard to really appreciate how much data capacity we have. Keep reading to find out just how big a gigabyte, a terabyte, and a petabyte are.

The Gigabyte = 1,024 Megabytes
We start with the lowly “byte”. In simplest terms, 1 byte is the amount of data needed to store 1 character (letter). If the average word is 6 characters long, then the average word is 6 bytes. For a 500-word essay, that’s 3,000 bytes. You need 1,024 bytes to have 1 kilobyte (KB). You may recognize the “kilo” prefix from similar terms like “kilometer” and “kilogram”, both of which mean “a thousand meters” and “a thousand grams” respectively. But because of the way computers are designed, the number 1,024 is used in place of 1,000. So a 500-word essay is 3,000 bytes, or 2.92 KB. A 200,000-word novel, then, would require 1,172 KB, or 1.14 megabytes (MB). The complete works of Shakespeare would take up approximately 5 MB of space in plain text format. 5 MB is also the average amount of space required for a 5-minute MP3 file.
 * A gigabyte (GB) is 1,024 MB.** That’s equivalent to 10 yards of books standing side by side. That’s 200 MP3 songs running at 5 minutes each. That’s a little bigger than the size of a feature film at standard definition. But most of us are already familiar with the term “gigabyte”. So what comes next?

The Terabyte = 1,024 Gigabytes
For a long time, hard drives were measured in GB. My 6-year-old laptop has an 80GB hard drive. My current desktop computer has a 300GB hard drive. But in the past few years, hardware developers have come out with 1- and 2-terabyte (TB) hard drives. How big of an improvement is this? Well, 1 TB = 1,024 GB = 1,048,576 MB = 1,073,741,824 KB = 1,099,511,627,776 bytes. In other words, a 1 TB hard drive has the capacity to hold **a trillion bytes**. That’s a far step up from floppy disks that only held **thousands** of bytes. Do you remember CD-ROMs? Way back before mp3 players and iPods and smartphones, music used to be sold and purchased on plastic laser-etched circles that would spin. These discs were large enough to hold 700 MB. How does that compare to the 1 TB hard drives of today? You would need approximately **1,500 CD-ROMs** to match the capacity of a 1 TB hard drive. Now, let’s say that the dimensions of a CD case are 142 mm x 125 mm x 8 mm (yes, I measured). If you stacked 1,500 CD cases on top of one another – and kept it from toppling over – it would reach a height of 12 meters, or 39 feet. You can enjoy all of that memory space within a compact metallic storage device now. Impressive.

The Petabyte = 1,024 Terabytes
And finally, we arrive at the newest data size that is slowly but surely becoming a norm in regular conversation – the petabyte (PB). The human brain reportedly has the ability to store about 2.5 petabytes of memories. The Large Hadron Collider generates around 15 petabytes of data every year. AT&T transfers approximately 20 petabytes of data through its network every day. When we talk about data capacities in this range, it becomes hard to visualize just how grand of a scale we’re talking about. If 1 TB is a trillion bytes, then 1 PB is **a quadrillion bytes**. In scientific notation, that’s 1015! Even as I write this, I’m having a hard time comprehending just how big that is. Our Milky Way Galaxy is home to approximately 2 hundred billion stars. If each individual star was a single byte, then we would need **5,000** Milky Way Galaxies to reach 1 PB of data. Or how about television? If we were to count using standard definition TV episodes, then 1 PB would amount to around 10,000 hours of TV programming. If you watched all of those episodes without ever stopping – not even to eat, drink, or sleep – it would take you 2 non-stop years to watch it all. This is the kind of capacity we have for data storage today. Quadrillions of bytes passing through our network cables right under our noses every second. Only 10 years ago, a single CD would hold maybe 20 MP3 songs; today, we can load up our HDDs and SSDs with thousands and thousands of songs easily. Technology has advanced in great ways and data storage is no exception. I hope this article has given you a glimpse of just how far we’ve come.