Conversion from Kilobits to 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.

Information about the Gigabit (Gbit)

The gigabit is a unit of digital information equal to one thousand million bits, or one billion in the short scale. Its symbol is Gbit. It is the unit that names the current standard of wired networking, and the word gigabit has become shorthand for a particular level of capability rather than merely a quantity.

Gigabit Ethernet, standardised in 1998 and 1999, carries one gigabit per second over ordinary twisted-pair copper cabling up to a hundred metres. It replaced the hundred-megabit standard that preceded it and remains the connection built into most computers, switches and routers. That single decision fixed the meaning of gigabit for a generation of engineers.

In octets, a gigabit is 125 megaoctets. A gigabit-per-second link therefore moves about 125 megaoctets each second in ideal conditions, so a two-gigaoctet film transfers in around sixteen seconds. Real transfers are slower because protocol overhead, disc speed and the far end of the connection all impose their own limits, and it is unusual for storage to keep up with the network at these rates.

Domestic fibre services now advertise gigabit speeds routinely, and in many countries the figure has become a marketing threshold rather than a technical one. Very few households can use it: a gigabit connection is enough to stream around two hundred high-definition video services at once. Its real benefit is not peak speed but headroom, since a link that is never near capacity has consistently low latency.

Memory chips are specified in gigabits for the same reason smaller ones are specified in megabits: the count reflects the number of storage cells on the die. An 8-gigabit chip holds one gigaoctet, and eight such chips make an 8-gigaoctet memory module. Flash memory follows the same convention, so a 512-gigabit flash die holds 64 gigaoctets.

Above the gigabit the scale continues in thousands. Ten-gigabit Ethernet is standard in data centres, forty and hundred-gigabit links join buildings and cities, and the backbone of the internet runs at multiples of these. Each step keeps the same relationship to the octet, and each step is quoted in bits per second because that is what the optics and the copper actually carry.

One gigabit equals 1,000,000,000 bits, 1,000 megabits, 125 megaoctets, or about 0.9313 gibibits.