A bitstream (or bit stream), also known as binary sequence, is a

sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is called ...

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

s. A bytestream is a sequence of

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...

s. Typically, each byte is an 8-bit quantity, and so the term octet stream is sometimes used interchangeably. An octet may be encoded as a sequence of 8 bits in multiple different ways (see bit numbering) so there is no unique and direct translation between bytestreams and bitstreams. Bitstreams and bytestreams are used extensively in

telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...

and

computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

. For example,

synchronous Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...

bitstreams are carried by

SONET Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diode ...

, and

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...

transports an

asynchronous Asynchrony is the state of not being in synchronization. Asynchrony or asynchronous may refer to: Electronics and computing * Asynchrony (computer programming), the occurrence of events independent of the main program flow, and ways to deal wit ...

bytestream.

Relationship between bitstreams and bytestreams

In practice, bitstreams are not used directly to encode bytestreams; a communication channel may use a signalling method that does not directly translate to bits (for instance, by transmitting signals of multiple frequencies) and typically also encodes other information such as framing and

error correction In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communi ...

together with its data.

Examples

The term bitstream is frequently used to describe the configuration data to be loaded into a

field-programmable gate array A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term ''Field-programmability, field-programmable''. The FPGA configuration is generally specifi ...

(FPGA). Although most FPGAs also support a byte-parallel loading method as well, this usage may have originated based on the common method of configuring the FPGA from a serial bit stream, typically from a serial

PROM A promenade dance, commonly called a prom, is a dance party for high school students. It may be offered in semi-formal black tie or informal suit for boys, and evening gowns for girls. This event is typically held near the end of the school y ...

flash memory Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both use ...

chip. The detailed format of the bitstream for a particular FPGA is typically proprietary to the FPGA vendor. In mathematics, several specific infinite sequences of bits have been studied for their mathematical properties; these include the Baum–Sweet sequence, Ehrenfeucht–Mycielski sequence,

Fibonacci word A Fibonacci word is a specific sequence of binary digits (or symbols from any two-letter alphabet). The Fibonacci word is formed by repeated concatenation in the same way that the Fibonacci numbers are formed by repeated addition. It is a para ...

, Kolakoski sequence, regular paperfolding sequence, Rudin–Shapiro sequence, and

Thue–Morse sequence In mathematics, the Thue–Morse sequence, or Prouhet–Thue–Morse sequence, is the binary sequence (an infinite sequence of 0s and 1s) obtained by starting with 0 and successively appending the Boolean complement of the sequence obtained thus ...

. On most

operating systems An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

, including

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

and

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...

, standard I/O libraries convert lower-level paged or buffered

file access In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

to a bytestream paradigm. In particular in Unix-like operating systems, each process has three

standard streams In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...

, that are examples of unidirectional bytestreams. The Unix pipe mechanism provides bytestream communications between different processes. Compression algorithms often code in bitstreams, as the 8 bits offered by a byte (the smallest addressable unit of memory) may be wasteful. Although typically implemented in low-level languages, some high-level languages such as Python and Java offer native interfaces for bitstream I/O. One well-known example of a

communication protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics (computer scien ...

which provides a byte-stream service to its clients is the

(TCP) of the

Internet protocol suite The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

, which provides a bidirectional bytestream. The

Internet media type A media type (also known as a MIME type) is a two-part identifier for file formats and format contents transmitted on the Internet. The Internet Assigned Numbers Authority (IANA) is the official authority for the standardization and publication o ...

for an arbitrary bytestream is . Other media types are defined for bytestreams in well-known formats.

Flow control

Often the contents of a bytestream are dynamically created, such as the data from the keyboard and other peripherals (/dev/tty), data from the pseudorandom number generator ( /dev/urandom), etc. In those cases, when the destination of a bytestream (the consumer) uses bytes faster than they can be generated, the system uses process synchronization to make the destination wait until the next byte is available. When bytes are generated faster than the destination can use them, there are several techniques to deal with the situation: * When the producer is a software algorithm, the system pauses the producer with the same process synchronization techniques. * When the producer supports flow control, the system only sends the ''ready'' signal when the consumer is ready for the next byte. * When the producer can't be paused—it is a keyboard or some hardware that doesn't support flow control—the system typically attempts to temporarily store the data until the consumer is ready for it, typically using a

queue __NOTOC__ Queue () may refer to: * Queue area, or queue, a line or area where people wait for goods or services Arts, entertainment, and media *''ACM Queue'', a computer magazine * ''The Queue'' (Sorokin novel), a 1983 novel by Russian author ...

. Often the receiver can empty the buffer before it gets completely full. A producer that continues to produce data faster than it can be consumed, even after the buffer is full, leads to unwanted

buffer overflow In information security and programming, a buffer overflow, or buffer overrun, is an anomaly whereby a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory locations. Buffers are areas of memory ...

packet loss Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion.Kur ...

network congestion Network congestion in data networking and queueing theory is the reduced quality of service that occurs when a network node or link is carrying more data than it can handle. Typical effects include queueing delay, packet loss or the blocking of ...

, and

denial of service In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connect ...

References

{{Reflist Data transmission Reconfigurable computing

Relationship between bitstreams and bytestreams

Examples

Flow control

See also

References