Jump to content

Data-rate units

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by TechControl (talk | contribs) at 00:21, 29 January 2009 (→Examples). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

In telecommunications, bit rate or data transfer rate is the average number of bits, characters, or blocks per unit time passing between equipment in a data transmission system. This is typically measured in multiples of the units bit per second or byte per second.

Bit rates (data-rate units)
Name Symbol Multiple
bit per second bit/s 1 1
Metric prefixes (SI)
kilobit per second kbit/s 103 10001
megabit per second Mbit/s 106 10002
gigabit per second Gbit/s 109 10003
terabit per second Tbit/s 1012 10004
Binary prefixes (IEC 80000-13)
kibibit per second Kibit/s 210 10241
mebibit per second Mibit/s 220 10242
gibibit per second Gibit/s 230 10243
tebibit per second Tibit/s 240 10244

Units

'k' vs 'Ki'

'k' and 'Ki' stand for 'kilo' and kibi respectively. They are prefixes to units where 'k' stands for 1,000 and 'Ki' stands for 1,024, because 'Ki' comes from its use in computing where 210 = 1,024. Unfortunately, 'K' is often incorrectly used instead of 'Ki'. Furthermore, the broad public not being necessarily aware of this subtle difference, usually uses 'Kbps' and 'Kibps' indiscriminately, creating confusion. Whenever 'Kibps' is used, it is usually accurate.

'b' vs 'B'

'b' stands for 'bit' and 'B' stands for 'byte', where one byte refers to 8 bits. This can lead to confusion, as when a "1 Mega" connection is advertised, it usually means 1 Mib/s (mebibit per second) or 1.049 Mb/s (megabit per second), meaning the maximum achievable download speed is actually about 128 KiB/s (kibibyte per second) or 131 kB/s (kilobyte per second).

Example usage

If the data rate of a data-stream is 8,192 bits per second, then using the different capitalization of letters this would be as follows:

8192 / 1000 = 8.192 kb/s
8192 / 1024 = 8 Kib/s
8192 / (8 x 1024) = 1 KiB/s
8192 / (8 x 1000) = 1.024 kB/s
8192 / 8 = 1024 B/s

Bytes are typically used in modern systems, but even when 8-bit bytes are used, the number of kbyte/s is not necessarily exactly one eighth the number of kbit/s because the count of bytes might not include framing bits. For example, a 56 kb/s RS-232 serial line transfers only 5.6 kbyte/s — not 7 kbyte/s — when used in the most common configuration (asynchronous, 8 data bits, no parity, one stop bit). It is fairly common to use kbyte/s with the binary meaning (1,024 byte/s) — more so than for kb/s — perhaps because of the close relationship with the common binary usage of kilobyte for measuring file sizes.

Notes about the related unit kibibit per second:

103 = 1,000 bit/s = 1 kb/s (one kilobit or one thousand bits per second)
210 = 1,024 bit/s = 1 Kib/s (one kibibit per second)

kbps is also commonly used for describing bit rates for streaming data such as video.


Related: kilobit/kibibit, kilobyte/kibibyte

bit

kilobit per second

A kilobit per second (kb/s or kbit/s or kbps) is a unit of data transfer rate equal to 1,000 bits per second. It is sometimes mistakenly thought to mean 1,024 bits per second, using the binary meaning of the kilo- prefix, though this is incorrect.[citation needed] 'K' means 1024, and 'k' means 1000.

Examples

Most digital representations of audio are measured in kb/s:

(These values vary depending on audio data compression schemes)

  • 4 kb/s – minimum achieved for encoding recognizable speech (using special-purpose speech codecs)
  • 8 kb/s – telephone quality
  • 32 kb/s – MW quality
  • 192 kb/s – Nearly CD quality for a file compressed in the MP3 format
  • 1,411 kb/s – CD audio (uncompressed, 16 bit samples × 44.1 kHz × 2 channels)

Megabit per second

A megabit per second (abbreviated as Mb/s or Mbit/s or Mbps) is a unit of data transfer rate equal to 1,000,000 bits per second. Because there are 8 bits in a byte, a transfer speed of 8 megabits per second (8 Mb/s) is equivalent to 1,000,000 bytes per second (approximately 977 Kib/s).

Usage examples

The bandwidth of consumer broadband internet services is often rated incorrectly in megabits (a unit of information) or more correctly in megabits per second; the formal abbreviation for megabit per second is Mbit/s. Note that in this context the term bandwidth is used colloquially to mean the data transfer rate.

Data streams representing compressed video are often measured in Mb/s:

  • 2.0 Mb/s — VHS quality
  • 8 Mb/s — DVD quality
  • 27 Mb/s — HDTV quality

Each DTV (Digital television) channel is permitted to be broadcast at a data rate up to 19 megabits per second (19 Mb/s), or 2.375 megabytes per second. However, the broadcaster does not need to use this entire bandwidth for just one broadcast channel. Instead the broadcast can be subdivided across several video subchannels of varying quality and compression rates, including non-video datacasting services that allow one-way high-bandwidth streaming of data to computers.[1]

More specific examples found on standard Comcast digital streams (transmitted in MPEG2 format):

  • 2-3 Mb/s — a low-definition digital channel with a very clean signal
  • 5-6 Mb/s — a low-definition digital channel with a digitized ("dirty") analog signal (or just an analog channel)
  • 8-12 Mb/s — a medium to high-definition digital channel with DVD quality data (equivalent to HBO-HD)
  • 18-20 Mb/s — a high-definition digital channel at 1080i (equivalent to Discovery HD)

Another example, Network cards and cables are typically available in 10/100/1000 Mb/s. This means they can support a transfer rate of 10 or 100 or 1000 Mb/s.

Gigabit per second

A Gigabit per second (Gb/s or Gbit/s or Gbps) is a unit of data transfer rate equal to 1,000 (103) megabits per second, 1,000,000 (106) kilobits per second or 1,000,000,000 (109) bits per second.

Examples of use:

Terabit per second

A terabit per second (Tb/s or Tbit/s or Tbps) is a unit of data transfer rate equal to 1,000 gigabits per second, 1,000,000 megabits per second, 1,000,000,000 kilobits per second, or 1,000,000,000,000 bits per second.

Examples of use:

"bibit"s

Because the computer's memory is fundamentally structured in binary units, multiples of the number 1024 (= 210) are more coherent with computer memory than the multiples of 10 or 100 or 1000 used in the common system of Arabic numerals. As a result, a series of names paralleling the "Kilo, Mega, Giga, Tera" units have been devised. These are: "Kibi, Mebi, Gibi, Tebi" (corresponding to 1024, 1,048,576 (= 10242), 1,073,741,824 (=10243), etc. Thus the binary equivalent to a Kilobit is a kibibit; the binary equivalent to a Megabit is a Mebibit, etc. These names give the impression of a "bibit" unit, which in itself does not exist.

kibibit per second

A kibibit per second (Kib/s) is a unit of data transfer rate equal to 1,024 bits per second.

Due to inconsistencies in the terminology, the word "kibibit" is not capitalized, though the abbreviation "Kibit" is.

Another unit of data transmission is the Kibibyte per second (KiB/s or Kibyte/s) which is 1,024 bytes per second. This is not necessarily exactly 8 Kib/s because the bit rate may include framing bits (see kilobit per second).

One Kibibit per second should not be confused with one kilobit per second:

103 b/s = 1,000 b/s = 1 kb/s (one kilobit or one thousand bits per second)
210 b/s = 1,024 b/s = 1 Kib/s (one kibibit or one thousand twenty-four bits per second)

The unit is useful in serial datarates:

57k6 = 57.600 kBd/s = 45 Kib/s (at a standard setting of 8N1)

Related: Kibibit, Kilobit, Kibibyte

Mebibit per second

A Mebibit per second (Mib/s or Mibit/s) is a unit of data transfer rate equal to 1,024 kibibits per second or 1,048,576 bits per second.

Another unit of data transmission is the mebibyte per second (MiB/s or Mibyte/s) and is eight times a mebibit per second:

1 MiB/s = 8 Mib/s

One mebibit per second should not be confused with one megabit per second:

106 b/s = 1,000,000 b/s = 1 Mb/s (one megabit or one million bits per second)
220 b/s = 1,048,576 b/s = 1 Mibit/s (one mebibit per second)

Related: Mebibit, Megabit, Mebibyte

Gibibit per second

A Gibibit per second (Gib/s) is a unit of data transfer rate equal to 1,024 mebibits per second or 1,048,576 kibibits per second or 1,073,741,824 bits per second.

Another unit of data transmission is the gibibyte per second (GiB/s or Gibyte/s) and is eight times a gibibit per second:

1 GiB/s = 8 Gib/s

One gibibit per second should not be confused with one gigabit per second:

109 bit/s = 1,000,000,000 bit/s = 1 Gb/s (one gigabit or one billion (milliard) bits per second)
230 bit/s = 1,073,741,824 bit/s = 1 Gib/s (one gibibit per second)

Related: Gibibit, Gigabit, Gibibyte

Tebibit per second

A Tebibit per second (Tib/s or Tibit/s) is a unit of data transfer rate equal to 1,024 gibibits per second, 1,048,576 mebibits per second, 1,073,741,824 kibibits per second, or 1,099,511,627,776 bits per second.

Another unit of data transmission is the tebibyte per second (TiB/s or Tibyte/s) and is eight times a tebibit per second:

1 tebibyte/s = 8 tebibit/s

One tebibit per second should not be confused with one terabit per second:

1012 bit/s = 1,000,000,000,000 bit/s = 1 Tb/s (one terabit or one million million bits per second)
240 bit/s = 1,099,511,627,776 bit/s = 1 Tib/s (one tebibit per second)

Related: Tebibit, Terabit, Tebibyte.

byte

kilobyte per second

A kilobyte per second (kB/s or kBps) is a unit of data transfer rate equal to:

Megabyte per second

A Megabyte per second (MB/s or MBps) is a unit of data transfer rate equal to:

Computer data interfaces are often rated in MB/s:

  • PATA 33 – 133 MB/s
  • SATA 150 – 300 MB/s
  • PCI 133 – 533 MB/s

Related: Megabyte, Mebibit, Mebibyte

Gigabyte per second

A Gigabyte per second (GB/s or GBps) is a unit of data transfer rate equal to:

Conversion formulas

To convert between common denotations, the following formula are used.

kb/s → KiB/s((n * 1000) / 8) / 1024 = m
kb/s → MB/m((((n * 1000) / 8) / 1024) / 1024) * 60 = m
kb/s → MB/h(((((n * 1000) / 8) / 1024) / 1024) * 60) * 60 = m

The following table shows how much data would theoretically be downloaded when running such a stream in more common denotations.

kb/s50.00150.00139.81
KiB/s6.1018.3117.07
MB/m0.361.071.00
MB/h21.4664.3760.00

Table

name symbol b/s B/s example
bit per second b/s 1 1/8
byte per second B/s 8 1
kilobit per second kb/s 1000 = 10^2 125 = 10^2/8
Kibibit per second Kib/s 1024 = 2^10 128 = 2^10/8
kilobyte per second kB/s 8000 = 8*10^2 1000 = 10^2
Kibibyte per second KiB/s 8192 = 8*2^10 1024 = 2^10

Examples

quantity unit b/s B/s description
56 kb/s 56,000 7,000 56k modem - 56 kb/s - 56,000 b/s
64 kb/s 64,000 8,000 64k ISDN - 64 kb/s - 64,000 b/s [3]
128 kb/s 128,000 16,000 128 kb/s MP3 - 128,000 b/s [4]
1536 kb/s 1,536,000 192,000 1536k T1 - 1,536,000 b/s (1.536 Mb/s)
/ kb/s Most digital representations of audio are measured in kb/s: (These values vary depending on audio data compression schemes)
4 kb/s 4,000 500 minimum achieved for encoding recognizable speech (using special-purpose speech codecs)
8 kb/s 8,000 1,000 telephone quality
32 kb/s 32,000 4,000 MW quality
192 kb/s 192,000 24,000 Nearly CD quality for a file compressed in the MP3 format
1,411.2 kb/s 1,411,200 176,400 CD audio (uncompressed, 16 bit samples × 44.1 kHz × 2 channels)
/ Mb/s Video data
2 Mb/s 2,000,000 250,000 VHS quality
8 Mb/s 8,000,000 1,000,000 DVD quality
27 Mb/s HDTV quality
1 Gb/s Gigabit Ethernet
5 Gb/s 5,000,000,000 625,000,000 USB 3.0
10 Gb/s 10 gigabit Ethernet
? Gb/s SCSI & Fibre Channel hard drives
1.244 Gb/s OC-24, a 1.244 Gb/s SONET data channel
9.953 Gb/s OC-192, a 9.953 Gb/s SONET data channel
39.813 Gb/s OC-768, a 39.813 Gb/s SONET data channel, the fastest in current use
1 Tb/s SEA-ME-WE 4 submarine cable - 1.28 terabits per second<ref>"Fujitsu Completes Construction of SEA-ME-WE 4 Submarine Cable Network". Fujitsu Press Releases. Fujitsu. 2005-12-13. Archived from the original on 2007-03-17. Retrieved 2008-01-31. {{cite web}}: Cite has empty unknown parameter: |1= (help)</ref>
/ MB/s Computer data interfaces are often rated in MB/s:
133 MB/s 1,064,000,000 133,000,000 PATA 33 - 133 MB/s
150 MB/s 1,200,000,000 150,000,000 SATA 1.5Gb/s - First generation
300 MB/s 2,400,000,000 300,000,000 SATA 3Gb/s - Second generation
600 MB/s 4,800,000,000 600,000,000 SATA 6Gb/s - Second generation
533 MB/s 4,264,000,000 533,000,000 PCI 133 - 533 MB/s

References

  1. ^ http://en.wikipedia.org/wiki/Digital_television
  2. ^ "Fujitsu Completes Construction of SEA-ME-WE 4 Submarine Cable Network". Fujitsu Press Releases. Fujitsu. 2005-12-13. Archived from the original on 2007-03-17. Retrieved 2008-01-31. {{cite web}}: Cite has empty unknown parameter: |1= (help)

See also

Retrieved from "https://en.wikipedia.org/w/index.php?title=Data-rate_units&oldid=267087532"