If you bought a 256GB drive and your computer shows 238GB, and you wondered if the capacity had somehow shrunk, it's because two different counting systems are at play.
Manufacturer (base 1000) vs. OS (base 1024)
Storage manufacturers calculate capacity using base 1000: 1GB = 1,000MB = 1,000,000,000 bytes. Operating systems like Windows and macOS instead calculate using base 1024: 1GB = 1024MB = 1,073,741,824 bytes.
Why 256GB shows up as 238GB
Dividing 256,000,000,000 bytes (the manufacturer's 256GB) by the base-1024 figure (1,073,741,824) gives about 238. The drive isn't defective or misrepresented — the two sides are just counting differently.
The technically correct unit: GiB
To avoid this confusion, the base-1024 unit is formally called a GiB (gibibyte). In practice, though, most operating systems still just label it "GB," so the confusion persists.
Which base to use when converting
Use base 1000 when reasoning about a drive's advertised (packaging) capacity, and base 1024 when predicting what your computer will actually display — understanding both explains why the two numbers never match.
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