# Bit time

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{{Short description|Time it takes to send a bit from one network host to another}}
{{See also|Slot time}}
{{Use American English|date = March 2019}}
'''Bit time''' is a concept in [computer network](/source/computer_network)ing.<ref name="x113">{{cite web | title=Definition of bit time | website=PCMAG | url=https://www.pcmag.com/encyclopedia/term/bit-time | access-date=2025-06-23}}</ref> It is defined as the time it takes for one bit to be ejected from a [network interface controller](/source/network_interface_controller) (NIC) operating at some predefined standard speed, such as 10&nbsp;Mbit/s.<ref name="h822">{{cite book | last=Dye | first=Mark | last2=McDonald | first2=Richard | last3=Rufi | first3=Antoon | title=Network Fundamentals, CCNA Exploration Companion Guide | publisher=Cisco Press | date=2007-10-29 | isbn=978-0-13-287743-5 }}</ref> The time is measured between the time the [logical link control](/source/logical_link_control) sublayer receives the instruction from the [operating system](/source/operating_system) until the bit actually leaves the NIC. The bit time has nothing to do with the time it takes for a bit to travel on the network medium but has to do with the internals of the NIC. Typically this refers to the smallest usable reference time, often also referred to as the 'minimum time quantum'.<ref name="y207">{{cite book | last=Paret | first=Dominique | title=Multiplexed Networks for Embedded Systems | publisher=John Wiley & Sons | date=2007-06-13 | isbn=978-0-470-51170-1 | page=90}}</ref><ref name="m371">{{cite book | last=Natale | first=Marco Di | last2=Zeng | first2=Haibo | last3=Giusto | first3=Paolo | last4=Ghosal | first4=Arkadeb | title=Understanding and Using the Controller Area Network Communication Protocol | publisher=Springer Science & Business Media | date=2012-01-19 | isbn=978-1-4614-0314-2 | page=5}}</ref>

To calculate the bit time at which a NIC ejects bits, use the following:

         bit time = 1 / NIC speed

To calculate the bit time for a 10&nbsp;Mbit/s NIC, use the formula as follows:
 
         bit time = 1 / (10 * 10^6)
                  = 10^-7
                  = 100 * 10^-9
                  = 100 nanoseconds

The bit time for a 10&nbsp;Mbit/s NIC is 100&nbsp;nanoseconds. That is, a 10&nbsp;Mbit/s NIC can eject 1 bit every 0.1 microsecond (100 nanoseconds = 0.1 microseconds).

Bit time is distinctively different from [slot time](/source/slot_time), which is the time taken for a pulse to travel through the longest permitted length of network medium.

==References==
{{Reflist}}

Category:Ethernet
Category:Computer network analysis

{{network-stub}}

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Adapted from the Wikipedia article [Bit time](https://en.wikipedia.org/wiki/Bit_time) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Bit_time?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.