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 represented a ...

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 unit ...

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 tha ...

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 bitstreams are carried by SONET, 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 common ...

transports an asynchronous 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 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-programmable''. The FPGA configuration is generally specified using a hardware ...

(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 or

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 u ...

chip. The detailed format of the bitstream for a particular FPGA is typically proprietary to the FPGA vendor. In mathematics, several specific

infinite sequences 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 calle ...

of bits have been studied for their mathematical properties; these include the Baum–Sweet sequence, Ehrenfeucht–Mycielski sequence, Fibonacci word, Kolakoski sequence, regular paperfolding sequence, Rudin–Shapiro sequence, and Thue–Morse sequence. On most operating systems, 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 ...

, standard I/O libraries convert lower-level paged or buffered file access 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 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 sui ...

, which provides a bidirectional bytestream. The Internet media type 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 In Unix-like operating systems, and are special files that serve as cryptographically secure pseudorandom number generators. They allow access to environmental noise collected from device drivers and other sources. typically blocked if there ...

), 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. 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, packet loss,

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 ...

, and denial of service.

References

{{Reflist Data transmission Reconfigurable computing

Relationship between bitstreams and bytestreams

Examples

Flow control

See also

References