Data rate units
From Wikipedia, the free encyclopedia
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 | ||
|---|---|---|
| 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 |
[edit] kilobit per second
A kilobit per second (kbit/s or kb/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.
[edit] Examples
- 56k modem — 56,000 bit/s
- 128 kbit/s MP3 — 128,000 bit/s [1]
- 64k ISDN — 64,000 bit/s [2]
- 1536k T1 — 1,536,000 bit/s (1.536 Mbit/s)
Most digital representations of audio are measured in kbit/s:
(These values vary depending on audio data compression schemes)
- 4 kbit/s – minimum achieved for encoding recognizable speech (using special-purpose speech codecs)
- 8 kbit/s – telephone quality
- 32 kbit/s – MW quality
- 192 kbit/s – Nearly CD quality for a file compressed in the MP3 format
- 1,411 kbit/s – CD audio (uncompressed, 16 bit samples × 44.1 kHz × 2 channels)
[edit] Related units
[edit] '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 'kbps' indiscriminately, creating confusion. Whenever 'Kibps' is used, it is usually accurate.
[edit] '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 Mibit/s (mebibit per second) or 1.049 Mbit/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).
[edit] Example usage
If the data rate of a data-stream 8,192 bits per second, then using the different capitalization of letters this would be as follows:
8192 / 1000 = 8.192 kbit/s
8192 / 1024 = 8 Kibit/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 kbit/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 kbit/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 kbit/s (one kilobit or one thousand bits per second)
- 210 = 1,024 bit/s = 1 Kibit/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
[edit] Megabit per second
A megabit per second (abbreviated as 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 Mbit/s) is equivalent to 1,000,000 bytes per second (approximately 976 kB/s).
[edit] 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 Mbit/s:
More specific examples found on standard Comcast digital streams (transmitted in MPEG2 format):
- 2-3 Mbit/s — a low-definition digital channel with a very clean signal
- 5-6 Mbit/s — a low-definition digital channel with a digitized ("dirty") analog signal (or just an analog channel)
- 8-12 Mbit/s — a medium to high-definition digital channel with DVD quality data (equivalent to HBO-HD)
- 18-20 Mbit/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 Mbit/s. This means they can support a transfer rate of 10 or 100 or 1000 Mbit/s.
[edit] Interface and device speeds
| Interface | Megabits per second | Megabytes per second |
|---|---|---|
| USB Low speed (USB 1.x, 2.0) | 1.5 Mbit/s | 0.18 MB/s |
| USB Full speed (USB 1.x, 2.0) | 12 Mbit/s | 1.5 MB/s |
| USB High speed (USB 2.0) | 480 Mbit/s | 60 MB/s |
| USB Super speed (proposed) | 4.8 Gbit/s | 600 MB/s |
| Firewire 400 (IEEE 1394) | 400 Mbit/s | 50 MB/s |
| Firewire 800 (IEEE 1394b) | 800 Mbit/s | 100 MB/s |
| CD-ROM, 1x | 1.2 Mbit/s | 0.15 MB/s |
| CD-ROM, 52x | 62.4 Mbit/s | 7.8 MB/s |
| DVD-ROM, 1x | 11.1 Mbit/s | 1.3 MB/s |
| DVD-ROM, 16x | 177.3 Mbit/s | 21.1 MB/s |
| BD-ROM, 1x | 36 Mbit/s | 4.5 MB/s |
| SATA I | 1200 Mbit/s | 150 MB/s |
| SATA II | 2400 Mbit/s | 300 MB/s |
| PCIe, 1x | 2000 Mbit/s | 250 MB/s |
Note that these raw bit rates do not account for protocol, encoding, or other overheads; so they aren't even the theoretical peak data rates of these interface technologies.
Related: Megabit, a unit of information storage (as opposed to transmission), Gigabit Ethernet
[edit] Gigabit per second
A Gigabit per second (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:
- Gigabit Ethernet, 1 Gbit/s
- 10 gigabit Ethernet, 10 Gbit/s
- SCSI & Fibre Channel hard drives
- OC-24, a 1.244 Gbit/s SONET data channel
- OC-192, a 9.953 Gbit/s SONET data channel, the fastest in current use
[edit] Related units
Another unit of data transmission is the gigabyte per second (GB/s, GBps, or Gbyte/s), equal to 8 gigabits per second.
[edit] Terabit per second
A terabit per second (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.[1]
Examples of use:
- SEA-ME-WE 4 submarine cable - 1.28 terabits per second[2]
[edit] Related units
Another unit of data transmission is the terabyte per second (TB/s), equal to 8 terabits per second.
[edit] kibibit per second
A kibibit per second (Kibit/s) is a unit of data transfer rate equal to 1,024 bits per second.
[edit] Related units
Another unit of data transmission is the kibibyte per second (Kibyte/s or KiB/s) which is 1,024 bytes per second. This is not necessarily exactly 8 Kibit/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 bit/s = 1,000 bit/s = 1 kbit/s (one kilobit or one thousand bits per second)
- 210 bit/s = 1,024 bit/s = 1 Kibit/s (one kibibit or one thousand twenty-four bits per second)
The unit is useful in serial datarates:
Related: Kibibit, Kilobit, Kibibyte
[edit] Mebibit per second
A Mebibit per second (Mibit/s) is a unit of data transfer rate equal to 1,024 kibibits per second or 1,048,576 bits per second.
[edit] Related units
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 Mibit/s
One mebibit per second should not be confused with one megabit per second:
- 106 bit/s = 1,000,000 bit/s = 1 Mbit/s (one megabit or one million bits per second)
- 220 bit/s = 1,048,576 bit/s = 1 Mibit/s (one mebibit per second)
Related: Mebibit, Megabit, Mebibyte
[edit] Gibibit per second
A Gibibit per second (Gibit/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.
[edit] Related units
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 Gibit/s
One gibibit per second should not be confused with one gigabit per second:
- 109 bit/s = 1,000,000,000 bit/s = 1 Gbit/s (one gigabit or one billion bits per second)
- 230 bit/s = 1,073,741,824 bit/s = 1 Gibit/s (one gibibit per second)
Related: Gibibit, Gigabit, Gibibyte
[edit] Tebibit per second
A Tebibit per second (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.
[edit] Related units
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 Tbit/s (one terabit or one million million bits per second)
- 240 bit/s = 1,099,511,627,776 bit/s = 1 Tibit/s (one tebibit per second)
Related: Tebibit, Terabit, Tebibyte.
[edit] Megabyte per second
A Megabyte per second (MB/s or MBps) is a unit of data transfer rate equal to:
- 1,000,000 bytes per second, or
- 1,000 kilobytes per second, or
- 8 Megabits per second.
Computer data interfaces are often rated in MB/s:
Related: Megabyte, Mebibit, Mebibyte
[edit] Conversion formulas
To convert between common denotations, the following formula are used.
| kbps → KBps | ((n * 1000) / 8) / 1024 = m |
|---|---|
| kbps → MBpm | ((((n * 1000) / 8) / 1024) / 1024) * 60 = m |
| kbps → MBph | (((((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.
| kbps | 50.00 | 150.00 | 139.81 |
|---|---|---|---|
| KBps | 6.10 | 18.31 | 17.07 |
| MBpm | 0.36 | 1.07 | 1.00 |
| MBph | 21.46 | 64.37 | 60.00 |
[edit] References
- ^ terabit - a definition from Whatis.com.
- ^ 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 on 2008-01-31.
