Division
Binary Weights & Measures
Instrument
Scale rule, dual system
Standard
IEC 80000-13
Drawing
Rev A
Ki

Measured shortfall between the byte
as sold and the byte as counted

A drive is sold in powers of ten and counted in powers of two. Nothing is missing from the hardware and nothing is wrong with the arithmetic. What goes missing is part of the number, and this drawing shows exactly which part.

Scale drawing of advertised capacity against counted capacity, with the shortfall hatched
Bytes shipped, decimal
As your computer counts it
Absent from the label
Of the quoted number
Notes
  1. Both readings are correct. The manufacturer shipped 1012 bytes and called it a terabyte, which is what the SI prefix means. Your computer divided by 240 and printed the letters TB anyway, which is what it has always done.
  2. A standard exists and is ignored. IEC 80000-13 defined the kibibyte, mebibyte, gibibyte and tebibyte in 1998 precisely to end this. Adoption is complete in principle and absent in practice.
  3. One machine uses both systems at once. Memory is sold in powers of two, storage in powers of ten, and network throughput in decimal bits. No component is at fault and every component disagrees.
  4. The matter has been litigated. Suits were brought in the United States against drive manufacturers over this exact arithmetic and were settled. No storage was created.
Detail A · unit belonging to neither system

The Division exhibits the 3.5-inch diskette as the worst object in its collection. Its capacity is 1,440 kibibytes. To reach the number printed on the label, the industry divided that by 1,000.

PropertyValue
Printed on the label1.44 MB
Actual capacity1,474,560 bytes
In decimal megabytes1.47 MB
In binary mebibytes1.41 MiB
Prefix as used1024 × 1000

The megabyte on that label is neither decimal nor binary but a third quantity, invented once and printed several hundred million times. The Division has classified it as a unit of history and declines to calibrate against it.

Drawn by
The Division
Checked by
Nobody
Scale
Two, simultaneously
Reconciled
No