| Mebibits (Mibit) | Pebibits (Pibit) |
|---|---|
| 1 Mebibit | 9.31322574615 × 10-10 Pibit |
| 2 Mebibits | 0.00000000186264514923 Pibit |
| 3 Mebibits | 0.00000000279396772385 Pibit |
| 4 Mebibits | 0.00000000372529029846 Pibit |
| 5 Mebibits | 0.00000000465661287308 Pibit |
| 10 Mebibits | 0.00000000931322574615 Pibit |
| 20 Mebibits | 0.0000000186264514923 Pibit |
| 25 Mebibits | 0.0000000232830643654 Pibit |
| 50 Mebibits | 0.0000000465661287308 Pibit |
| 100 Mebibits | 0.0000000931322574615 Pibit |
| Reference | Mebibits (Mibit) | Pebibits (Pibit) |
|---|---|---|
| A plain text message (160 characters) | 0.0012207 Mibit | 1.13687 × 10-12 Pibit |
| A three-minute MP3 | 22.8882 Mibit | 0.0000000213163 Pibit |
| A smartphone photo | 30.5176 Mibit | 0.0000000284217 Pibit |
| A high-definition film | 30517.6 Mibit | 0.0000284217 Pibit |
| A dual-layer Blu-ray disc | 381470 Mibit | 0.000355271 Pibit |
The mebibit is a unit of digital information equal to 1,048,576 bits, which is 1,024 kibibits or two to the twentieth power. Its symbol is Mibit. It is the binary counterpart of the megabit, and the difference between the two has grown to 4.9 per cent — small enough to be ignored casually, large enough to matter in a specification.
Its natural home is semiconductor memory, where capacity is fixed by the address lines on the chip. A memory die with twenty address bits can reach exactly 1,048,576 locations, so densities land on powers of two rather than on round decimal numbers. A chip described as 512 megabits in a catalogue is very often 512 mebibits in reality, which is 537 megabits, and the datasheet is where the truth is written.
That habit is old and deliberate. Semiconductor manufacturers have always sized memory in binary because the wiring makes any other choice wasteful: an address bus is a fixed number of lines, and using only part of the range it can reach throws away silicon. Storage manufacturers had no such constraint, which is precisely why the two industries diverged.
For a sense of quantity, a mebibit is 131,072 octets, or about 128 kibioctets. That is roughly the contents of a long book as plain text, or a single low-resolution image. In network terms it is a hundredth of a second of a gigabit link.
The IEC prefixes were introduced in 1998 partly because at this level and above the approximation stops being safe. Buying a component described as one megabit and receiving one mebibit is a five per cent surprise; at the tebibit the same confusion is a ten per cent surprise, and in a contract for a data centre that is a real sum of money.
Correct usage is now common in standards documents, in hardware datasheets and in operating system internals, and rare in advertising and consumer software. The best rule when reading a figure is to ask which industry produced it: if it describes memory or a chip, assume binary; if it describes storage or a link, assume decimal.
One mebibit equals 1,048,576 bits, 1,024 kibibits, 131,072 octets, or about 1.049 megabits.
The pebibit is a unit of digital information equal to 1,125,899,906,842,624 bits, which is 1,024 tebibits or two to the fiftieth power. Its symbol is Pibit. It is the binary counterpart of the petabit, and the gap between them has widened to 12.6 per cent.
That widening is worth watching, because it is the whole argument for the IEC prefixes in one number. Each step up the ladder multiplies the discrepancy by 1.024, so what began as a harmless 2.4 per cent at the kibibit is an eighth of the quantity here and a fifth at the yobibit. A convention that was reasonable for small numbers becomes indefensible for large ones.
A pebibit is 140,737,488,355,328 octets, or 128 tebioctets. Storage of this size exists in supercomputer memory systems, in the fastest scientific data buffers and in the aggregate memory of very large clusters. The largest machines on the list of the world's fastest computers have main memory measured in pebioctets, and the ability to hold an entire simulation in memory rather than on disc is what makes certain calculations feasible at all.
Because these systems are addressed in binary, the binary unit is the correct one and the decimal figure would be an approximation. A cluster with a pebibit of memory does not have a petabit; it has 12.6 per cent more, and a scheduler that allocated on the decimal figure would leave that much unused.
The unit also appears in filesystem limits. Several widely used filesystems have maximum volume or file sizes expressed as exact powers of two, and where those limits fall in this range they are naturally written in pebibytes or pebioctets. Documentation that converts them to decimal units loses the property that made them memorable.
In everyday computing the pebibit is never encountered. It belongs to specifications, to system architecture and to the design of the largest machines, and a converter needs it for exactly those documents. Anywhere the underlying quantity is a power of two, this is the unit that says so without rounding.
One pebibit equals 1,024 tebibits, 140,737,488,355,328 octets, or about 1.126 petabits.