Your hard drive may be reporting a smaller number for a few reasons, but the first thing you should know is that you probably aren’t being “scammed” out of data — that number is completely normal. Here’s why.
External Drives Often Come With Software Installed
The first (but less important) explanation is that many external drives come with backup software from the manufacturer. Generally, we recommend getting rid of it, as it’s rarely better than the stuff you can download online (such as our favourite backup program Crashplan). So while it probably won’t free up heaps of space, you should probably format that drive before you do anything else.
If you’re a Windows user, just right-click on the drive in Windows Explorer and choose “Format”. Format it to NTFS if you’re planning on storing a lot of data (like music or a backup), and FAT32 or ExFAT if you plan on using it to transport files between Macs and Windows PCs.
If you’re a Mac user, go to /Applications/Utilities/Disk Utility and click on the drive in the left sidebar. Click the “Erase” tab in the middle pane, then choose your file system from the dropdown. Mac OS Extended (Journaled) is the best default option for storing a lot of data, but FAT32 and ExFAT are better if you’re using it on both Mac and Windows.
Once you’ve formatted it, you won’t have those annoying software popups when you plug it in, and you should have a bit of extra free space on the drive.
Hard Drives Are Measured One Way, Marketed Another Way
Here’s the bigger reason you have less space: computers are based on binary maths, which means storage is counted using base 2 — not base 10, which is what you see on the box. So a kilobyte is actually 1024 bytes, not 1000, which is what it says on the box. Similarly, a megabyte is 1024 kilobytes, a gigabyte is 1024 megabytes and so on. That means the actual amount of space on the drive is going to be lower than what it’s marketed as, with the difference being bigger as you get to bigger drives. In general, for each gigabyte reported on the box, you’ll have about 70MB less space, which means that your 1TB drive has closer to 900GB.
There isn’t much you can do about this, unfortunately. If you’re a Mac or Linux user, you should update your software, since more recent versions of OS X (10.6 and up) and Ubuntu (10.10 and up) actually use base 10 to report storage space and file sizes, which should make it easier for you to judge (that’s also why if you move a file from a Windows machine to a Mac the file will appear bigger even though it isn’t — it’s being measured with base 10). Unfortunately, there’s no way to “fix” the problem in Windows — you just need to know that you’ll get a little less space than what you see on the box and act accordingly. If you have 1000GB of data, a 1TB drive won’t be enough, and you’ll want to buy a 1.5TB instead. It doesn’t matter whether it’s internal, external, or even a thumb drive — this affects every kind of drive out there.
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