Why 1TB hard drive but shows only 931GB

How many times have you unboxed a new computer, phone, or drive, only to be shocked to find out that it doesn’t have as much storage space as it says on the box? That 512GB SSD can really only use 477GB, or the 1TB hard drive can only have 931GB of space left.

Why 1TB hard drive but only 931GB of actual capacity

There are a few main reasons why this is happening. Let’s see why the advertised capacity on the drive is often not the same as the actual capacity.

Operating system and pre-installed applications

The most basic reason why the actual disk space is lower than you expect is because the drive already has some data in it when you buy it. This is not the case with removable drives like flash drives or SD cards, but is a staple for phones and computers with built-in.

When you buy a computer, the operating system (such as Windows or macOS) takes up a large portion of the space. These operating system files are essential for the system to run, so you should not touch them.

For example, on my system, the folder C:Windows takes up 25GB. That’s about a tenth of the entire available disk space.

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However, it’s not just operating system files that take up space. Most operating systems include additional applications that you install. This includes everything from Windows 10 bloatware to macOS built-in apps like GarageBand.

While they are not technically part of the operating system, they come with it and therefore take up space. You can usually delete these to reclaim hard drive space.

How computers measure hard drive space

While pre-installed apps are certainly often important, the biggest reason you’re not getting the full amount advertised is because computers measure numbers differently than humans.

Binary Number Interpretation

The calculator uses standard value prefixes, including “kilo” for thousand, “mega” for million, “giga” for billion, “tera” for trillion, and so on.

Everyone, including hard disk manufacturers, uses the decimal system, the system of measuring numbers with base 10. So when we say “500 gigabytes,” they mean 500 billion. bytes.

However, computers use binary with base 2, where all numbers are 1 or 0. If you are unfamiliar, here is a list of numbers 1-10 written in binary:


As you can see, in binary, 2^1 represents the decimal value 1, 2^2 equals 4, 2^3 equals 8, 2^4 equals 16, etc. Each position of the new digit in the The binary system increases the value of the number to a power of two. 2^10, equals 1.024.

Binary and decimal measurement

We now know why computers use 1,024 instead of 1,000 to identify these common prefixes. For a computer, a kilobyte is 1,024 bytes, not 1,000 bytes as it is for a human. As with other values, a megabyte is 1,024 kilobytes and a gigabyte is 1,024 megabytes.

Let’s take a few examples to make it easier to understand, let’s say you buy a 250 GB SSD. That drive holds 250,000,000,000 bytes, but the computer doesn’t display it that way.

Going backwards, we can divide by 1,024 three times (once to convert bytes to kilobytes, again to convert kilobytes to megabytes, and the last time to convert megabytes to gigabytes) to see what this actually is. is how much:

250,000,000,000 / (1,024 * 1,024 * 1,024) = 232,830,643,653 bytes, or 232.83GB

Testing a 250GB drive in Windows shows that its maximum capacity is 232GB, exactly as we calculated. Takes about 18GB more than advertised.

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And the larger the disk, the larger the difference between the measured space and the real space. For example, a 1TB (1,000GB) drive has 931GB of space.

Gigabytes and Gibibytes

So why is there such a difference? Why don’t hard drive manufacturers provide real capacity when advertising? Technically, they do.

The correct definition of “kilo” is to the power of 1,000 and that of 1.024 is “kibi.” The International Electrotechnical Commission has published standards for the measurement of data in binary to resolve this confusion.

While a kilobyte (KB) represents 1,000 bytes, a kibibyte (KiB) represents 1,024 bytes. It’s the same for mebibyte (MiB), gibibyte (GiB), tebibyte (TiB), etc.

For some reason, Windows uses the “GB” prefix incorrectly, but it measures space in gibibytes. Other operating systems, like macOS, accurately measure 1GB as a billion bytes. Thus, the same 250GB drive connected to the Mac will have a total capacity of 250GB.

Additional drive partitions

In addition to the above, another potential cause of the decrease in total disk space is additional partitions.

In case you don’t know, you can separate physical drives into different logical parts, called partitions. Partitioning the hard drive allows you to install two different operating systems on one drive, like dual booting between Windows and Linux.

Manufacturers often install a recovery partition on the drive, which allows you to reset your system in the event of a catastrophic failure. Like any other data, these files take up space on the drive. But since recovery partitions are usually hidden from standard view, you can’t see them.

To view these partitions on your drive in Windows, right-click the Start menu or press Win + X and select Disk Management. Here you can see each drive on your system and the partitions that make up it. If you partition named Restore, Recovery or similar, it’s your recovery partition.

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In most cases, you can delete these partitions and get that space back. However, it is best not to do so. They make restoring your system a lot easier, and reclaiming a small amount of space isn’t worth the hassle of manually restoring your system.

Hidden features also use hard drive space

Finally, most operating systems contain features that take up space but don’t exist as actual files. For example, the Windows Shadow Copy service is used to provide resources for Previous Versions and the System Restore function.

System Restore allows you to roll back to an earlier point in time if your system is not functioning properly, while Previous Versions keeps a copy of your personal files so you can undo the changes. Of course, both need space to function.

To view and change the hard drive space usage of the Shadow Copy features, press Win + Pause to quickly open the menu About in the Settings app. From here, click System protection on the right side. In the window that appears, select your drive from the list and select Configure.

You will see a new dialog box that allows you to completely disable bsystem protection (although I do not recommend this). Below you’ll see your current usage and can adjust the maximum amount that Windows uses. Somewhere around 10 percent is pretty.

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Now you know how the computer calculates hard drive space

The factors discussed here explain the difference between advertised and actual storage space on phones, drives, or other storage devices. In addition, you should not use the commands in this article because it can damage the hard drive.

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