Conversion from Gibibits to Kilobits

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.

Information about the Kilobit (kbit)

The kilobit is a unit of digital information equal to one thousand bits. Its symbol is kbit. The lowercase k matters: it marks the decimal kilo of the metric system, one thousand exactly, as distinct from the binary 1,024 that the capital K sometimes indicated in older computing usage.

That distinction was fought over for decades. Memory is built in powers of two, so a chip holding 1,024 bits was called a kilobit chip, and the name stuck even though the number was wrong by 2.4 per cent. Storage and transmission, meanwhile, always counted in true thousands. The IEC settled the matter in 1998 by naming the binary quantity a kibibit, leaving the kilobit to mean one thousand and nothing else.

For a sense of scale, a kilobit holds 125 octets, which is about 125 characters of unaccented text — roughly a long sentence, or the length of a short social-media post. A single low-resolution photograph is thousands of times larger. The kilobit is a unit for things that were once considered generous and are now considered trivially small.

Its historical home was the telephone modem. Dial-up connections were rated in kilobits per second, and the numbers marked the era precisely: 300 bits per second in the late 1970s, then 1.2, 2.4, 9.6, 14.4, 28.8 and finally 56 kilobits per second, the last of which pushed an ordinary voice line to its theoretical ceiling. Anyone who used the internet before broadband measured their experience in these numbers.

The kilobit survives in audio and video encoding, where bit rates are quoted in kilobits per second. Speech codecs used in telephony run from 8 to 64. Music encoded at 128 kilobits per second was the early standard for portable players, 192 and 256 are common now, and 320 is the practical ceiling for the older lossy formats. Video runs a decimal order higher, in megabits.

Memory chip capacities are still occasionally described in kilobits, particularly for small serial memories used in embedded devices, where a 64-kilobit part holds 8 kilooctets of configuration data. In those specifications the figure is usually the binary one, so the datasheet is worth reading carefully.

One kilobit equals 1,000 bits, 125 octets, or about 0.9766 kibibits.