Bit
of the titles of this article is ambiguous. For further meanings see bit (term clarifying). |
Repeated system of units international | ||||||
---|---|---|---|---|---|---|
of bit SI | binary | |||||
name | symbol | repeated | name | symbol | repeated | |
k-bit | kbit | 10^{ 3} (or 2^{ 10}) | kibibit | Kibit | 2^{ 10} | |
megabit | Mbit | 10^{ 6} (or 2^{ 20}) | mebibit | Mibit | 2^{ 20} | |
gigabit | Gbit | 10^{ 9} (or 2^{ 30}) | gibibit | Gibit | 2^{ 30} | |
terabit | Tbit | 10^{ 12} (or 2^{ 40}) | tebibit | Tibit | 2^{ 40} | |
petabit | Pbit | 10^{ 15} (or 2^{ 50}) | Pibit | 2 | 50^{ pebibit} | |
exabit | public exhibition for multimedia | 10^{ 18} (or 2^{ 60}) | exbibit | Eibit | 2^{ 60} | |
zettabit | Zbit | 10^{ 21} (or 2^{ 70}) | zebibit | Zibit | 2^{ 70} | |
yottabit | Ybit | 10^{ 24} (or 2^{ 80}) | yobibit | Yibit | 2^{ 80} |
the term bit in computer science and information technology as well as related fields of activity in different connections is used. Both the use and the way of writing (bit or bit) are non-uniform thereby and vary in the literature; some frequently,but always not used conventions are in the section way of writing. This concerns a word crossing out bi nary digi t, English for binary digit. The term became of the mathematician John W. Tukey probably 1946, after othersSources already 1943 suggested. The term was mentioned in writing 1948 for the first time on page 1 work A Mathematical Theory OF Communication famous of Claude Shannons. It is common to all use ways in connection with information and information technology that a bit orbit as a measure for the size and/or. the extent by data or information one regards.
Possible uses are (there the large and lower case varied, are refrained here from a distinction):
- A bit as memory cell
- bit as unit for one Data set (see also rivet or Hartley).
- The bit as unit for the information content (see also Shannon).
Table of contents |
representation of bits in digital technique
a bit is the smallest information unit. Each information is bound to a storage medium. The information capacity 1 bit corresponds to the information, which of two possible occurencesapplies. The following exemplary circumstances can store thus an information capacity of a bit:
- The position of a switch with two conditions, for example a light switch with the positions or out.
- The switching status of a transistor, „slight resistance “ or „high resistance “.
- The presence of a tension, which is larger or smaller than a given value.
- A variable, which one of two values, for example 0 or 1, the logical logical values true or wrong, high or low, H or L contained can.
The value one or several bits is generally called in computer science condition, since a bit in the use of a physical element, for example, is represented to the mentioned transistor, which onecertain condition possesses. If several elements are built up to a unit, the total condition of this unit of the condition of each individual element depends and again several different conditions of this unit result.
binary notation; Bit and byte
with nBits can different conditions^{ be represented} 2 n, then for example a unit from two bits can be in four different conditions: 00, 01, 10 and 11. Further 16 different conditions can be stored with four bits,with eight bits 256, and so on. Each additional bit doubles the number of possible representable conditions. If these conditions represent whole numbers by coding in the binary system, then a bit is the weightier (specializedlinguistically: with higher order), the further left it instands for the written down bit sequence (see also notational system).
Modern computers and storage media have storage capacities of billions of bits. Memory capacities are indicated therefore in other units. Generally one uses here the byte ( a Oktett of eight bits) asBasic unit and powers of 2^{ 10} (= 1024) as unit prefixes (details see byte). Within the range of the long-distance data transmission however the bit held itself as basic unit with the indication of the data transmission rate - ISDN transfers maximally 64 kbit/s (64,000 bits perSecond) on a utilizable channel, nearly Ethernet 100 Mbit/s (100 million bit per second). Differently than with the byte one adheres here strict to the SI system for prefixes.
Besides the bit is used as unit:
- for the indication of the capacity individual storage media (here however with binary prefixes); Example: a 512-Mb-Chip (megabit, not to confound with MT) stores 2^{ 29} bits = 2^{ 26} bytes, thus 64 MT, of it eight pieces on a memory latch plate results in a 512-MB DIMM
- for bus widths and/or. thoseProcessing versatility on chip level (reason for it is the possibility of operations bit by bit and/or. the principle of transmission bit by bit)
bit error and forward error correction
general applies in the digital world that there are none „unimportant “bits. Examples:
- two 64 bit numbers are unequal,even if they only in the niederwertigsten bit differ. That leads for example to a confidence problem, if two digitized finger marks are compared, and the program is not so written that it can deal with small differences „more intelligently “.
- an executable filebecomes usually uselessly, even if only one bit „tilts “, if thus from 0 falsely a 1 or turned around.
- Only one error in the bit sequence 2048 bits of a long key to a coded text leads inevitably to the fact thatthe text any longer to decode does not leave itself (see cryptology).
- Bit errors on audio CDs can be tolerated and led maximally to noise errors; on data CDs they are fatal, why these additional error correcting codes contain.
So seen it can happen that only oneBit crucially is for acceptance or refusal, success or failure, in safety-relevant systems as for instance in space travel even for lives or death.
One can answer to the fact that only a wrong bit is sufficient, in order to produce unexpected results, thereby,that one information redundantly codes. The simplest kind of the redundant coding consists of it, a data block as check total the binary checksum adding the parity bit in such a way specified. The odd-even check makes it possible to determine, if in the block wrongly transfer an individual bitbecame. If an error arose, the receiver can request a new transmission (so for instance in the TCP/IP - minutes).
If more than a redundant bit per data block is added, one speaks of forward error correction (forward error correction, FEC); it becomes with some data media andwith many communication procedures assigned and it permits to correct incorrectly picked out and/or received bits as long as the error rate remains underneath a critical threshold. Like that for example CD is each byte distributed and also over a distance of 2 cm onother bytes together than Reed Solomon code stored, so that CD mm-touch arbitrary 1 be missing can and the whole information nevertheless are present. The price for the forward error correction is the storage location (or the transmission band width) for the redundant bits - the storage locationfrom CDs would approx. be without such measures. 17% more largely, networks 40% faster, mobile telephones 200% higher performance, with last the two differently depending upon type.
the coded information itself often contains data compression redundancy. By different Compressing procedure can be accommodated the appropriate information on substantially less storage location. See in addition also entropy coding.
Depending upon kind of the information thereby also a lossy compression is possible, which reduces additionally the storage requirement. The information loss becomes insignificant thereby as (relative)regards - that is particularly with picture and clay/tone data possible
way of writing
the word bit is capitalized, if it concerns the designation of physical bits. For example: The data bus possesses width of 16 bits. ThoseIndication of data rates (bits per second) is smallwritten. For example: Ethernet 10BaseT with a data rate of 10 Mbit/s.
power modes
depending upon Verwendungsgebiet the indication of the bit quantity takes place in different power modes. This can lead in particular then to mistakes,if the used basis no longer indicated, but only overall of k-bit, megabit etc. one speaks. With stored data sets power-of-two numbers are usually used, so that 1 Kbit = 2^{ 10} bits = 1024 are bits. One notes thatthe resolution K is capitalized and also not as Kilo is expressed, but only as approx. With transferred data sets per time unit however powers of ten are taken as a basis, so that 1 kbit/s = 10^{ 3} bit/s = 1000 bit/s (1 k-bit/second) are. Similar one Differences result for Mbit and Mbit/s, GBit and GBit/s etc. The meant power is when using terms such as k-bit, megabit etc. not clearly evidently from the connection, then one should indicate her explicitly.
Qubits inthe quantum communication theory
the bit must be differentiated by the Qubit (quantum bit), which is used in the quantum communication theory.