Data-rate units: Difference between revisions
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Revision as of 10:53, 2 December 2010
 | This article's factual accuracy is disputed. (November 2010) |
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.
| 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 |
Avoiding confusion
- See also Bit rate for the differences between gross bitrate and net bitrate and between throughput and goodput.
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 abbreviation "2 MB" can be expanded in 2 different ways as well ("mega-" vs. "mebi-" and "-byte"). 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 700% 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", 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'. However, it has been suggested [by whom?] that 'bit' should not be abbreviated since it's already an abbreviation for "binary digit", and the difference between bit and byte can lead to confusion. 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
 | This section may require copy editing for style, tone, and grammar. (November 2010) |
In 1999, the International Electromechanical Commission (IEC) published Amendment 2 to “IEC 60027-2: Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics”;. This standard, which had been approved in 1998, introduced the prefixes kibi-, mebi-, gibi-, tebi-, pebi-, exbi-, to be used in specifying binary multiples of a quantity. The names come from the first two letters of the original SI prefixes followed by bi which is short for “binary”. It also clarifies that, from the point of view of the IEC, the SI prefixes only have their base-10 meaning and never have a base-2 meaning.
So this is the correct usage for file, disk, memory size:
Kilobytes (KB) 1.000 Kibibyte (KiB) 1024 Megabyte (MB) 1.000 ^ 2 Mebibyte (MiB) 1024 ^ 2 Gigabyte (GB) 1.000 ^ 3 Gibibyte (GiB) 1024 ^ 3 Terabyte (TB) 1.000 ^ 4 Tebibyte (TiB) 1024 ^ 4 Petabyte (PB) 1.000 ^ 5 Pebibyte (PiB) 1024 ^ 5
The problem is: the industry has not adopted these standards. If Windows shows the size of a disk, it converts 28.735.078.400 bytes to “26.7 GB”. It should be either 28.7 GB, or 26.7 GiB. Remember the 1.44MB floppy? It actually never existed: it is either 1.40MiB or 1.47MB.
On September 18, 2003, Reuters has reported that Apple, Dell, Gateway, Hewlett-Packard, IBM, Sharp, Sony, and Toshiba have been sued in a class-action suit in Los Angeles Superior Court for “deceiving” the true capacity of their hard drives. This of course was due to ambiguity of “GB” when used by software and hardware vendors. This precedent might prompt Apple to adapt binary prefixes in its Mac OS, as well as other companies to put pressure on Microsoft to adapt them in its Windows operating systems.
One could argue: people have always used the MB = 1024*1024 for disk drives, why change now? Well, clarity is a good reason, and unambiguity.
Decimal multiples of bits
Kilobit per second
A kilobit per second (kbit/s or 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 or 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 or 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 "Kibit" 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
Kilobyte per second
A kilobyte per second (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
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 formulae
| 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 [1] |
| 133 | MB/s | 1,064,000,000 | 133,000,000 | Computer data interfaces | PATA 33 – 133 MB/s |
| 150 | MB/s | 1,200,000,000 | 150,000,000 | Computer data interfaces | SATA 1.5Gb/s – First generation |
| 300 | MB/s | 2,400,000,000 | 300,000,000 | Computer data interfaces | SATA 3Gb/s – Second generation |
| 600 | 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 |
See also
Notes
- ^ "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.
References
- International Electrotechnical Commission (2007). "Prefixes for binary multiples". Retrieved on 2007-05-06.
- IEC 60027-2 "Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics+