Why does a formatted drive have less space than advertised? – News Block

SSD Samsung 850 EVO with M.2 SSD and SATA 2 hard drive
Corbin Davenport / Instructional Geek

Formatted drives may appear to have less space than advertised due to different byte sizes, hidden partitions, SSD over-provisioning, and pre-installed bloatware.

A gallon of milk is a gallon of milk, but a terabyte of hard drive space may not be what it says on the box! The difference between advertised and reported disk capacities is easy to explain.

The most common reason: different counting methods!

Drive manufacturers use a different way of calculating storage capacity than some operating systems. Specifically, Microsoft Windows (along with many other programs) counts storage space in binary bytes, while drive manufacturers use decimal bytes.

The difference between decimal and binary bytes is that decimal bytes are based on the decimal (base 10) system while binary bytes are based on the binary (base 2) system. In the decimal system, the basic unit of measurement for digital data storage is the decimal kilobyte, which is equal to 1000 bytes. In the binary system, there are 1024 bytes in a binary kilobyte.

As a result, 1 GB may be slightly less than 1 GB when displayed in Windows. That’s because 1 GB in the decimal system equals 1000 megabytes, but in the binary system it equals 1024 megabytes. When displayed on a Windows computer, this would be rounded down to slightly less than 1 GB. When you add up all those 24-megabyte differences, Windows reports the formatted size for a 1TB drive as 931GB.

By the way, the terms kibibyte, mebibyte, and gibibyte are used to specifically indicate binary units.

Hidden partitions

Hidden disk partitions are parts of a disk that are reserved for specific purposes, such as storing the operating system and system files or creating a recovery partition. When displayed in the operating system, these partitions are invisible to the user and are not included in the drive’s available capacity.

As a result, when a drive is formatted, the capacity of hidden partitions is not included in the total available capacity, which means that the formatted drive may appear to have less space than advertised. For example, suppose a drive with a capacity of 1TB has a hidden partition that takes up 500GB of space. The formatted drive will only appear to have 500GB of available space, even though the advertised capacity was 1TB.

Some manufacturers may create hidden partitions on the drive for pre-installed software or other files, which will also reduce the available capacity of the formatted drive.

SSD overprovisioning

Solid state drive (SSD) overprovisioning is the practice of reserving a portion of the drive’s capacity for use by internal drive processes, such as garbage collection, wear leveling, and power management. bad blocks. This reserved portion of the drive is invisible to you and is not included in the drive’s available capacity when displayed by the operating system.

Sometimes your SSD will have utility software that will allow you to change the over-provisioning level and even turn it off.


The advertised capacity of the drive may not include space used by any preinstalled software or other files that come with the drive. If the drive has such files, they will take up some of the available space, resulting in a formatted drive with less capacity than advertised.

This is most common with external hard drives that come with various software packages pre-installed, often on a partition that you can’t easily remove. However, any prebuilt computer or laptop is likely to have more than just the operating system installed.

you are not being fooled

While you may not have access to all of the space on your hard drives, there is no conspiracy to steal your drive space here. Regardless of how the unit sizes are reported, the actual number of bits you get does not change. Only the way they are grouped into larger units is different.

RELATED: Delete the recovery partition on your PC and take control of your hard drive

As for hidden partitions and bloatware, you can always remove both and get your space back. It’s your computer, after all, you can make the rules!

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