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.

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 vs -byte). The difference in the associated numbers can be significant:

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:

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 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

Examples

See also

• Binary prefix
• Bit rate
• List of device bandwidths
• Orders of magnitude (data)
• SI prefix

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

• 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+
• Donald Knuth: "What is a kilobyte?"