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Did you know: why a 1TB SSD shows 931GB in Windows

Did you know: why a 1TB SSD shows 931GB in Windows

Did you know that when you install a 1TB SSD and open "This PC" in Windows, it shows only about 931GB? Many people think space is missing or the drive is fake, but the truth is much simpler: the difference is in how the capacity is counted, not in the drive.

Manufacturers count in decimal

Drive makers measure capacity in decimal units, the same way as metres and kilograms: 1 kilobyte = 1,000 bytes, 1 gigabyte = 1,000,000,000 bytes, and 1 terabyte = 1,000,000,000,000 bytes (10 to the power of 12). According to NIST, this is the correct use of the SI prefixes.

Windows counts in binary

Windows divides by 1,024 instead of 1,000 at every step. So its "gigabyte" is 1,024 × 1,024 × 1,024 = 1,073,741,824 bytes. The catch is that it labels the result GB, even though it is really a different unit called GiB (gibibyte).

Let's do the maths:

  • 1,000,000,000,000 bytes ÷ 1,073,741,824 = about 931.3
  • That is why Windows shows a 1TB SSD as roughly 931GB.
  • The same goes for 2TB, which shows as about 1.81TB in Windows.

Same number of bytes, just two different units with almost the same name.

Where do KiB, MiB and GiB come from?

To clear up the confusion, the International Electrotechnical Commission (IEC) approved names for binary units in December 1998: kibi (KiB), mebi (MiB), gibi (GiB) and tebi (TiB), according to NIST. So 1GiB = 1,024 mebibytes, while 1GB = 1,000 megabytes. Many programs, Windows included, still write GB when they mean GiB.

What about Mac?

Apple has reported storage in decimal since Mac OS X Snow Leopard, so a 1TB drive shows close to 1TB on a Mac. According to Apple, older systems such as OS X Leopard and earlier, and iOS 10 and earlier, reported capacity in binary. That is why the same drive can show two different numbers on two computers.

Some space goes elsewhere too

Besides the counting difference, a few things take away from the space you can actually use:

  • Formatting: the file system reserves a small part to organise data.
  • Operating system: if it is your system drive, Windows, its files and updates take up part of it.
  • Recovery partitions: some PCs have hidden partitions for recovery and booting.

How to check your drive is fine

  1. Open the drive's properties in Windows and look at the full byte count next to the capacity.
  2. If it is close to 1,000,000,000,000 bytes for a 1TB drive, the drive is healthy and the capacity is all there.
  3. To estimate what Windows will show, multiply the capacity on the box by about 0.931.

What this means when you buy

If your games are large, remember that the space Windows shows is about 7% lower than the number on the box. If you want a fast 1TB SSD for your system and games, here is our pick:

Check the current price on the product page. Installments are available through Tamara and Tabby.

Bottom line

931GB is not missing space or a fake drive: it is the same 1TB counted a different way. Manufacturers count in thousands, while Windows counts in 1,024s and calls them GB. Need help choosing the right SSD? Message us on WhatsApp at +966 56 412 1558 or visit our Olaya or Aqiq branch in Riyadh. Installments are available through Tamara and Tabby.

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