How much disk space is "a lot?"
When I bought my first personal computer in 1987 it came with a five megabyte hard drive. In those days that was "a lot" of disk space and that drive cost about $500. So in 1987 disk space cost about $100 per megabyte.
Ten years later, in 1997, "a lot" of disk space would have meant something like five gigabytes -- that's 500 megabytes or 100 times as much storage as I had in 1987. In 1997 a five gigabtye drive cost around $600 dollars. So the cost per megabyte had fallen to about one dollar.
In 2006 a typical new computer comes with 200 gigabytes of disk space and you can buy drives of this size for around $70. But that's a minimal amount of storage, having "a lot" of disk space in 2006 means something like 700 gigabytes. And you can purchase a 700 gigabyte drive for under $400. That's a cost per megabyte of around 6 cents.
So in 2006 disk space costs about 1/2000th of what it did in 1987. And it's not just that computer storage has become cheaper, the drives are also much smaller. These days you can even carry a significant portion of your work around in your pocket on a jump drive (also called a thumb drive). These drives use a special kind of memory that doesn't require power, so there's no disk involved, and you can find a one-gigabyte jump drive for as little as $25.
This begs the question; "what we are putting on these immense hard drives?"
In this Bit Literate guide we are going to help you answer that question using an an online worksheet you can use to estimate how much space you are using, and how much you might need in the future. You'll also be able to see what kinds of files are taking up most of the space.
To start, click the link below to access the worksheet. When you're done come back to this page and we'll try to answer a second question; how much disk space will be "a lot" in 2016?
If you need help with the worksheet, or if you want to get more information on the approach we're using, you can watch the video tutorial (also liked below). This worksheet presents the exercise in a form called a Fermi Problem. It's worth understanding how to solve problems like this. You run into them all the time even if you've never heard that name before.
Calculate what my disk is used for... (opens the worksheet in a new window)
View a video tutorial on how to use the worksheet (the tutorial opens in a new window)
Ok, you've estimated how your hard disk is being used, and you've viewed the tutorial to get some background on how Fermi problems work. Now we want to see how good we were at estimating our disk usage, with an eye toward improving our results. This is a common approach for solving problems like this. Start with a rough estimate and then refine it until it's accurate enough for the intended purpose. We've provided a second video tutorial that demonstrates how to determine the space actually used by the various types of files stored on your computer.
View a video tutorial of how to see how much space is in use on your computer (the tutorial opens in a new window)
How good was your estimate?
Were you off by 10%? 50%? 100%? More?
If you were off by 50% or less then your estimate was pretty good. You have a good general idea of the types of files on your computer and how big those files are. You could easily go back to the worksheet and play with the numbers to make your prediction fit closely with reality.
But what if you were off by 100% or more? For example, what if you estimated that you are using ten gigabytes of disk space but when you checked you found that it is actually 50 gigabytes. That would mean that you were off by a factor of five or 500%. This level of error probably means that you made an error in the units you used in the estimate, or perhaps it means that our model (the worksheet represents a simple mathematical model) doesn't accurately reflect how your disk space is used. It is a simplistic model so maybe you have large files of some type that is being completely overlooked. Of course it could also be that one of your kids has a couple hundred music videos stashed away on the computer and that you didn't know about.
Fermi problems like this one are an example of a simple mathematical model. And when we work with mathematical models it's important to find some way to check the estimates and prove or disprove that the model provides a good representation of reality.
Now let's turn to a different question. How much disk space can we expect a typical computer to have in the year 2016? And what kind of files will be on that disk?
We've created an Excel spreadsheet you can download and use to produce an estimate of disk space in 2016. And of course there's a video. This one demonstrates how the spreadsheet can be used to make the prediction.
Download the Excel Spreadsheet
View a video tutorial that explains how to predict disk capacity in the year 2016
Data Source: Historical Notes about the Cost of Hard Drive Storage
Using the worksheet we've predicted that a personal computer in 2016 will have around one petabtye of of disk space. That's 1000 terabtyes and a terabtye is 1000 gigabytes. So if you have a 100 gigabtye drive today that means you could have 10,000 times as much space in 2016. That might seem outlandish until you remember that from 1987 to 2006 the amount of space available grew by
Which leads back to our final question, what will all that space be used for?
Unfortunately there's no mathematical model that can help us answer this one and the magic eight ball is notoriously unreliable. But we can make some guesses based on what has happened in the past, and on what we know about technologies that are expected to appear in the near future. For one thing we are likely to have huge video files on our computers. Today, feature films are distributed on DVDs and they commonly use three to four gigabtyes of disk space. In 2016 you might have dozens or even hundreds of movies on your computer, and high definition movies are likely to be much larger in the future. So if a high-def movie takes a 100 gigabytes, and you have 100 of them, you've used 100 terabytes of storage. That's 1/10 th of your drive.
And who knows how much space you'll need when it becomes possible to transmit high quality video directly from your cell phone to your PC, or when you have a home security system capturing video 24 hours a day, or after your carpal tunnel has finally caught up with you and you interact with your computer by talking to it.
We can't predict the future but we do know that few people, if any, could have predicted 1987 what personal computers would be capable of in 2006.
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