Data rate units


Data rate units

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 unit bit per second or byte per second.

Bit rates
Decimal prefixes (SI)
Name Symbol Multiple
kilobit per second kbit/s 103
megabit per second Mbit/s 106
gigabit per second Gbit/s 109
terabit per second Tbit/s 1012
Binary prefixes (IEC 60027-2)
kibibit per second Kibit/s 210
mebibit per second Mibit/s 220
gibibit per second Gibit/s 230
tebibit per second Tibit/s 240

Contents

Avoiding confusion

To be as explicit as possible, both the prefix and the suffix of the unit must be known. For example, the abbreviation 2 Mb can actually be expanded in 2 different ways (mega- vs mebi- and -bit). The difference in the associated numbers can be significant:

Unit Bits Bits / 1,000,000
Mega-bit 1,000,000 1.0
Mebi-bit 1,048,576 1.05
Mega-byte 8,000,000 8.0
Mebi-byte 8,388,608 8.39

The table above shows an approximate 5% difference between the corresponding mega- and mebi- units with a 800% difference between -bit and -byte units. Explicitness in units is important because difference can become even larger across different prefix units).

Prefix: k vs Ki

k- stands for kilo, meaning 1,000, while Ki- stands for kilobinary ("kibi-"), meaning 1,024. The standardized binary prefixes such as Ki- were relatively recently introduced and still face low adoption. K- is often used to mean 1,024, especially in KB, the kilobyte.

Suffix: b vs B

b stands for bit and B stands for byte. In the context of data rate units, one byte refers to 8 bits. For example, when a 1 Mbps connection is advertised, it usually means that the maximum achievable download bandwidth is 1 megabit/s (million bits per second), which is actually 0.125 MB/s (megabyte per second), or about 0.1192 MiB/s (mebibyte per second).

Problems

In 1999, the International Electrotechnical Commission (IEC) published Amendment 2 to "IEC 60027-2: Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics." This standard, approved in 1998, introduced the prefixes kibi-, mebi-, gibi-, tebi-, pebi-, and exbi- to be used in specifying binary multiples of a quantity. The name is derived from the first two letters of the original SI prefixes followed by bi (short for binary). It also clarifies that the SI prefixes be used only to mean powers of 10 and never powers of 2.

The correct use for file, disk, and memory size is as follows:

Unit (SI) Bytes Unit (IEC 60027-2) Bytes
Kilobyte (kB) 1,000 Kibibyte (KiB) 1,024
Megabyte (MB) 1,0002 Mebibyte (MiB) 1,0242
Gigabyte (GB) 1,0003 Gibibyte (GiB) 1,0243
Terabyte (TB) 1,0004 Tebibyte (TiB) 1,0244
Petabyte (PB) 1,0005 Pebibyte (PiB) 1,0245

Computer and technology industries have yet to adapt to these standards. When Microsoft Windows shows the size of a drive or a file, it uses powers of 1,024 but uses SI prefixes so that, for example, 28,735,078,400 bytes displays as 26.7 GB instead of either 28.7 GB, or 26.7 GiB.

The commonly advertised (formatted) capacity of the 3.5-inch floppy disk was 1.44 MB but was actually 1,440 KiB or 1.44 × 1,000 × 1,024 bytes, giving either 1.41 MiB or 1.47 MB.

On September 18, 2003, Reuters reported that Apple, Dell, Gateway, Hewlett-Packard, IBM, Sharp, Sony, and Toshiba were being sued in a class-action law-suit in the Los Angeles Superior Court for "deceiving" buyers as to the true capacity of those companies' hard drives. This of course was due to ambiguity of GB when used by software and hardware vendors.

Decimal multiples of bits

Kilobit per second

A kilobit per second (kbit/s, kb/s, or kbps) is a unit of data transfer rate equal to:

  • 1000 bits per second or
  • 125 bytes per second.

Megabit per second

A megabit per second (Mbit/s, Mb/s, or Mbps; not to be confused with mbit/s which means, literally, millibit per second) is a unit of data transfer rate equal to:

  • 1,000,000 bits per second or
  • 1,000 kilobits per second or
  • 125,000 bytes per second.

Gigabit per second

A gigabit per second (Gbit/s, Gb/s, or Gbps) is a unit of data transfer rate equal to:

  • 1,000 megabits per second or
  • 1,000,000 kilobits per second or
  • 1,000,000,000 bits per second or
  • 125,000,000 bytes per second

Binary multiples of bits

Kibibit per second

A kibibit per second (Kibit/s or Kib/s) is a unit of data transfer rate equal to 1,024 bits per second. The word "kibibit" is not capitalized, but the abbreviation "Kibits" is.

Mebibit per second

A mebibit per second (Mibit/s or Mib/s) is a unit of data transfer rate equal to:

  • 1,048,576 bits per second or
  • 1,024 kibibits per second.

Gibibit per second

A gibibit per second (Gibit/s or Gib/s) is a unit of data transfer rate equal to:

  • 1,073,741,824 bits per second or
  • 1,048,576 kibibits per second or
  • 1,024 mebibits per second.

Tebibit per second

A tebibit per second (Tibit/s or Tib/s) is a unit of data transfer rate equal to:

  • 1,099,511,627,776 bits per second or
  • 1,073,741,824 kibibits per second or
  • 1,048,576 mebibits per second or
  • 1,024 gibibits per second.

Decimal multiples of bytes

WARNING: These units are often not used in the suggested ways! See section above, "Problems".

Kilobyte per second

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

  • 8,000 bits per second, or
  • 1,000 bytes per second, or
  • 8 kilobits per second.

Megabyte per second

(not to be confused with Mbps - Mega bits per second) A megabyte per second (MB/s or MBps) is a unit of data transfer rate equal to:

  • 8,000,000 bits per second, or
  • 1,000,000 bytes per second, or
  • 1,000 kilobytes per second, or
  • 8 megabits per second.

Gigabyte per second

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

  • 8,000,000,000 bits per second, or
  • 1,000,000,000 bytes per second, or
  • 1,000,000 kilobytes per second, or
  • 1,000 megabytes per second, or
  • 8 gigabits per second.

Terabyte per second

A terabyte per second (TB/s or TBps) is a unit of data transfer rate equal to:

  • 8,000,000,000,000 bits per second, or
  • 1,000,000,000,000 bytes per second, or
  • 1,000,000,000 kilobytes per second, or
  • 1,000,000 megabytes per second, or
  • 1,000 gigabytes per second, or
  • 8 terabits per second.

Binary multiples of bytes

Kibibyte per second

A kibibyte per second (KiB/s or KiBps) is a unit of data transfer rate equal to:

  • 1,024 bytes per second, or
  • 8 kibibits per second, or
  • 8192 bits per second.

Mebibyte per second

A mebibyte per second (MiB/s or MiBps) is a unit of data transfer rate equal to:

  • 1,048,576 bytes per second, or
  • 1,024 kibibytes per second, or
  • 8 mebibits per second, or
  • 8192 kibibits per second, or
  • 8,388,608 bits per second.

Gibibyte per second

A gibibyte per second (GiB/s or GiBps) is a unit of data transfer rate equal to:

  • 1,073,741,824 bytes per second, or
  • 1,048,576 kibibytes per second, or
  • 1,024 mebibytes per second, or
  • 8 gibibits per second, or
  • 8192 mebibits per second, or
  • 8,388,608 kibibits per second, or
  • 8,589,934,592 bits per second.

Tebibyte per second

A tebibyte per second (TiB/s or TiBps) is a unit of data transfer rate equal to:

  • 1,099,511,627,776 bytes per second, or
  • 1,073,741,824 kibibytes per second, or
  • 1,048,576 mebibytes per second, or
  • 1,024 gibibytes per second, or
  • 8 tebibits per second.
  • 8192 gibibits per second, or
  • 8,388,608 mebibits per second, or
  • 8,589,934,592 kibibits per second, or
  • 8,796,093,022,208 bits per second.

Conversion formula

Name Symbol bit per second byte per second bit per second (formula) byte per second (formula)
bit per second bit/s 1 0.125 1 1/8
byte per second B/s 8 1 8 1
kilobit per second kbit/s 1,000 125 103 103/8
kibibit per second Kibit/s 1,024 128 210 27
kilobyte per second kB/s 8,000 1,000 8x103 103
kibibyte per second KiB/s 8,192 1,024 213 210
megabit per second Mbit/s 1,000,000 125,000 106 106/8
mebibit per second Mibit/s 1,048,576 131,072 220 217
megabyte per second MB/s 8,000,000 1,000,000 8x106 106
mebibyte per second MiB/s 8,388,608 1,048,576 223 220
gigabit per second Gbit/s 1,000,000,000 125,000,000 109 109/8
gibibit per second Gibit/s 1,073,741,957 134,217,728 230 227
gigabyte per second GB/s 8,000,000,000 1,000,000,000 8x109 109
gibibyte per second GiB/s 8,589,934,592 1,073,741,824 233 230
terabit per second Tbit/s 1,000,000,000,000 125,000,000,000 1012 1012/8
tebibit per second Tibit/s 1,099,511,627,776 137,438,953,472 240 237
terabyte per second TB/s 8,000,000,000,000 1,000,000,000,000 8x1012 1012
tebibyte per second TiB/s 8,796,093,022,208 1,099,511,627,776 243 240

Examples

Quantity Unit bits per second bytes per second Field Description
56 kbit/s 56,000 7,000 Networking 56k modem – 56 kb/s – 56,000 b/s
64 kbit/s 64,000 8,000 Networking 64k ISDN – 64 kb/s – 64,000 b/s
1536 kbit/s 1,536,000 192,000 Networking 1536k T1 – 1,536,000 b/s (1.536 Mb/s)
1 Gbit/s 1,000,000,000 125,000,000 Networking Gigabit Ethernet
10 Gbit/s 10,000,000,000 1,250,000,000 Networking 10 Gigabit Ethernet
1 Tbit/s 1,000,000,000,000 125,000,000,000 Networking SEA-ME-WE 4 submarine communications cable – 1.28 terabits per second [1]
4 kbit/s 4,000 500 Audio data minimum achieved for encoding recognizable speech (using special-purpose speech codecs)
8 kbit/s 8,000 1,000 Audio data telephone quality
32 kbit/s 32,000 4,000 Audio data MW quality
128 kbit/s 128,000 16,000 Audio data 128 kb/s MP3 – 128,000 b/s
192 kbit/s 192,000 24,000 Audio data Nearly CD quality for a file compressed in the MP3 format
1,411.2 kbit/s 1,411,200 176,400 Audio data CD audio (uncompressed, 16 bit samples × 44.1 kHz × 2 channels)
2 Mbit/s 2,000,000 250,000 Video data VHS quality
8 Mbit/s 8,000,000 1,000,000 Video data DVD quality
27 Mbit/s 27,000,000 3,375,000 Video data HDTV quality
1.244 Gbit/s 1,244,000,000 155,500,000 Networking OC-24, a 1.244 Gb/s SONET data channel
9.953 Gbit/s 9,953,000,000 1,244,125,000 Networking OC-192, a 9.953 Gb/s SONET data channel
39.813 Gbit/s 39,813,000,000 4,976,625,000 Networking OC-768, a 39.813 Gb/s SONET data channel, the fastest in current use
60 MB/s 480,000,000 60,000,000 Computer data interfaces USB 2.0
625 MB/s 5,000,000,000 625,000,000 Computer data interfaces USB 3.0
98.3 MB/s 786,432,000 98,304,000 Computer data interfaces FireWire IEEE 1394b-2002 S800
120 MB/s 960,000,000 120,000,000 Computer data interfaces Harddrive read, Samsung SpinPoint F1 HD103Uj [2]
133 MB/s 1,064,000,000 133,000,000 Computer data interfaces PATA 33 – 133 MB/s
188 MB/s 1,200,000,000 150,000,000 Computer data interfaces SATA 1.5Gb/s – First generation
375 MB/s 2,400,000,000 300,000,000 Computer data interfaces SATA 3Gb/s – Second generation
750 MB/s 4,800,000,000 600,000,000 Computer data interfaces SATA 6Gb/s – Third generation
533 MB/s 4,264,000,000 533,000,000 Computer data interfaces PCI 133 – 533 MB/s
1250 MB/s 10,000,000,000 1,250,000,000 Computer data interfaces Thunderbolt
8000 MB/s 64,000,000,000 8,000,000,000 Computer data interfaces PCI Express x16 v2.0
12000 MB/s 96,000,000,000 12,000,000,000 Computer data interfaces InfiniBand 12X QDR

See also

Notes

  1. ^ "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. http://web.archive.org/web/20070317223056/http://www.fujitsu.com/global/news/pr/archives/month/2005/20051213-01.html. Retrieved 2008-01-31. 
  2. ^ "Samsung overtakes". http://www.tomshardware.com/reviews/samsung-overtakes-a-bang,1730-9.html. 

References


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