(or bit stream
), also known as binary sequence
, is a sequence
is a sequence of bytes
. 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.
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.
The term bitstream is frequently used to describe the configuration data to be loaded into a field-programmable gate array
(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
chip. The detailed format of the bitstream for a particular FPGA is typically proprietary to the FPGA vendor.
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
offer native interfaces for bitstream I/O.
The Internet media type
for an arbitrary bytestream is application/octet-stream
. Other media types are defined for bytestreams in well-known formats.
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 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, and denial of service.
- ^ "Bitstream". Python Software Foundation. Archived from the original on 2016-09-08.
- ^ "Class BitSet". Oracle. Archived from the original on 2016-11-30.
Last edited on 27 December 2020, at 05:36
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