Conversion from Teraoctets to Gibibits

Information about the Teraoctet (To)

The teraoctet is a unit of digital information equal to one million million octets, or a thousand gigaoctets. Its symbol is To. It is the unit of the modern hard drive, and the point at which personal storage stopped being something anyone needed to manage carefully.

A teraoctet holds roughly two hundred and fifty thousand photographs from a phone, or two hundred hours of high-definition video, or a quarter of a million songs. For a person who is not a professional photographer or video editor, a single teraoctet is more storage than a lifetime of ordinary files will fill.

Consumer hard drives crossed one teraoctet in 2007 and now reach twenty or more. Solid-state drives arrived at the same capacities more slowly and at higher cost, but with far greater speed, and the two technologies now divide the market between capacity and performance rather than competing directly.

The teraoctet is where the decimal-binary discrepancy becomes visible enough to annoy. A drive sold as one teraoctet holds a million million octets exactly; the operating system divides by 1,024 four times and reports 0.909 tebioctets, which it usually labels as 931 gigaoctets. The shortfall appears to be 7 per cent, though nothing has actually been lost. At the petaoctet the same arithmetic produces a 12 per cent gap.

Backup and archiving live at this scale. A household's complete collection of photographs, documents and video typically fits in a few teraoctets, which is why external drives are sold in exactly that range. Cloud storage services price in teraoctets too, and the economics of keeping a second copy of everything only work because the unit price of storage has fallen faster than the quantity has grown.

In professional work the teraoctet is a daily quantity rather than a milestone. A day of filming in high resolution produces several teraoctets of raw footage. A genome sequencing run produces a few hundred gigaoctets, so a modest laboratory generates teraoctets a week. Both fields have had to build workflows around moving data that will not fit on any network in reasonable time.

One teraoctet equals 1,000,000,000,000 octets, 1,000 gigaoctets, 8 terabits, or about 0.9095 tebioctets.

Information about the Gibibit (Gibit)

The gibibit is a unit of digital information equal to 1,073,741,824 bits, which is 1,024 mebibits or two to the thirtieth power. Its symbol is Gibit. It is the binary counterpart of the gigabit, and the two now differ by 7.4 per cent — a gap wide enough that mistaking one for the other in a purchase order is a genuine error.

Its practical home is the memory industry. Dynamic memory chips are made in binary capacities because their internal organisation is a rectangular grid of rows and columns, both addressed in binary. A part described as 8 gigabits in marketing material is an 8-gibibit die, holding 8,589,934,592 bits, and eight of those make the 8 gibioctets a memory module advertises as 8 GB.

Flash memory follows the same rule for the same reason, though with a twist: flash dies include spare blocks to replace cells that wear out, so the usable capacity of a drive is deliberately less than the raw capacity of its chips. Manufacturers then quote the usable figure in decimal units, which is how a drive built from binary parts ends up labelled with a decimal number.

The 7.4 per cent gap explains a great deal of everyday confusion. A memory module of 8 gibioctets and a solid-state drive of 8 gigaoctets are not the same size, though both are written 8 GB. The module holds 8.59 gigaoctets; the drive holds 8.00. Nothing is wrong with either figure, but they are counted in different bases and cannot be compared without conversion.

A gibibit is 134,217,728 octets, or 128 mebioctets. In everyday terms that is roughly a hundred and thirty megaoctets — a couple of dozen photographs, or two minutes of high-definition video. It is not a large amount of data by modern standards, which is why the unit appears in component specifications rather than in descriptions of files.

The correct symbol, Gibit, is used in datasheets and in standards but almost never in advertising. When a document writes Gb without further explanation, the safe assumption is that memory means the binary quantity and networking means the decimal one, and that a careful writer would have written Gibit or Gbit to say which.

One gibibit equals 1,073,741,824 bits, 1,024 mebibits, 134,217,728 octets, or about 1.074 gigabits.