I recently purchased one 250 GB NVME Hard disk for my personal computer, but to my surprise, Windows 10 reported it as a 232.87 GB hard drive. Here are my findings on the reason behind this.
As you can see below, my hard disk - Kingston 250 GB NVME drive - detected in the device manager and showing under the Hard drives category.
In the Disk Management tool, the drive detected as Disk 0 but reported as 232.87 GB.
There is nothing wrong. The drive size mentioned by the manufacture is in Decimal standard(SI). That means 250GB is 250 Gigabytes.
When we convert that into Bytes...
250 Gigabyte = 250 x 1000^3 = 250 x 1000x1000x1000 = 250,000,000,000 Bytes.
But Windows reporting the size in Binary standard(IEC). ie, 232.78 GB is 232.87 Gibibyte(GiB).
Same in Bytes goes to..
232.87 Gibibyte = 232.87 x 1024^3 = 232.87 x 1024x1024x1024 = 250,042,258,554.88 Bytes
Both calculations resulted in an approximately equal number of bytes( there around 42Megabytes difference but it arguably due to the rounded GiB figure from Windows ). And when you convert directly 250 from Gigabyte to Gibibyte it is matching more accurately with what Windows is reporting.
250 GB = 232.83064365386962890625 GiB
In summary, most of the drive manufactures are advertising and mentioning the size of drives in Decimal standards (GB, TB, ..), whereas, in the Operating System(OS) level, the figures are displayed in Binary formats (GiB, TiB,..).
We should keep this reporting difference in mind while purchasing a drive and try to configure it in our computer system, otherwise, it may look like either the drive manufacturer or the OS trying to trick us.