Digital storage units explained
Two counting systems share the same prefixes. A kilobyte is a thousand bytes, a kibibyte is 1,024, and the gap widens at every step — which is the entire reason a new hard drive appears smaller than the box promised.
Bit bit
1 bit = 0.125 B Exact
A single binary digit, one or zero. Connection speeds are quoted in bits — a 100 Mbps line moves at best about 12.5 megabytes per second, because there are eight bits to a byte. The lowercase b in Mbps is doing a great deal of work.
Byte B
1 B = 1 B Exact
Eight bits, and historically the space for one character of text. It is still the atom of file sizes: everything above is a multiple of it, and the arguments are only ever about which multiple.
Kilobyte kB
1 kB = 1,000 B Exact
A thousand bytes in the decimal system used by drive manufacturers and networks. Windows will call 1,024 bytes a kilobyte instead, which is really a kibibyte. Both usages are so entrenched that the only safe move is to say which you mean.
Megabyte MB
1 MB = 1,000,000 B Exact
Exactly one million bytes. About a minute of MP3 audio, or a middling phone photo. The 4.9% gap against the mebibyte is where the confusion starts, and it only grows from here.
Gigabyte GB
1 GB = 1,000,000,000 B Exact
A billion bytes. Phone storage, RAM and data allowances are all quoted in gigabytes, though RAM is genuinely sold in binary units — a 16 GB memory stick really holds 16 GiB, while a 16 GB phone does not.
Terabyte TB
1 TB = 1,000,000,000,000 B Exact
A trillion bytes. This is where the decimal-versus-binary gap becomes visible to ordinary users: a 1 TB drive shows up as about 931 GB in Windows, and nothing is missing. The manufacturer counted in powers of ten and the operating system divided by 1,024 four times.
Petabyte PB
1 PB = 1,000,000,000,000,000 B Exact
A thousand terabytes. The scale of large research datasets and of what a serious streaming service adds to its library in a year. Rarely something an individual encounters outside a press release.
Kibibyte KiB
1 KiB = 1,024 B Exact
Exactly 1,024 bytes — two to the tenth. The binary units were given proper names in 1998 precisely to end this argument, and adoption has been patchy: Linux uses them, macOS switched to decimal, and Windows kept the old labels on the new maths.
Mebibyte MiB
1 MiB = 1,048,576 B Exact
1,048,576 bytes. About 4.9% more than a megabyte. If a file manager and a website disagree about a download size by roughly this much, this is why.
Gibibyte GiB
1 GiB = 1,073,741,824 B Exact
1,073,741,824 bytes, about 7.4% more than a gigabyte. RAM is genuinely measured this way because memory addressing is binary — which is why memory comes in 8, 16 and 32 GB rather than 10 or 20.
Tebibyte TiB
1 TiB = 1,099,511,627,776 B Exact
About 1.1 trillion bytes, roughly 10% more than a terabyte. This is the exact size of the gap that makes a new drive look short-changed, and it is the largest binary unit most people will ever meet.