Storing or transmitting information can use coded symbols {coding, computer} {encoding, computer} {decoding}.
types
Codes can use binary numbers, decimal numbers, words, images, and switches. Code size depends on possible-symbol number and probability.
probability
Symbols can have equal or unequal probability. Binary code use symbols 0 and 1, with equal probability. Probability is base-2 logarithm: P = - log(2^1) = 1/2 for one position. Information {average unexpectedness} is greatest if all symbols are equally probable.
information
Information measurement uses binary units. For binary code, with two equal-probability symbols, information in one position is 1 bit, 2^1 = 2. Information in three positions is 3 bits, 2^3 = 8, with eight possible series, such as 010.
Machines store and transmit data in record sets {block, data}| containing 2000, 4000, or 8000 bytes in fixed-length or variable-length blocks. Longer data blocks have fewer recombinations and can process faster.
Message or information packets {packet, information} {information packet} {message, information} are only for recipients that can decode them, using same methods as for encoding. Communication requires similarities between senders and receivers. Messages must have marks to show that they are messages. Messages reflect coding method.
If several inputs or outputs are waiting for transmission, CPU sends blocks in the most-efficient way {message switching} {block switching}.
Binary messages can split into sections and recombine many times, using methods {Data Encryption Standard} (DES) encoded in 56-bit keys. Methods can use three different keys {triple DES}.
Data can separate into small chunks, travel in pieces through different channels, and then reassemble {multiplexing, data}|.
Message can split into parts that take alternate routes and then recombine at delivery {packet switching}|. In modems, packets are strings of 8-bit bytes, each with start and stop bit.
Decimal-number input can convert to binary numbers {packing, data} {data, packing}. Binary numbers can convert to decimal-number output {unpacking}.
Data can travel on carrier frequencies by AM or FM, or data can be in pulses {ultrawideband}| (UWB).
Codes {ANSI code} can use 7, 8, or 9 bits to represent 128 or 256 printable and unprintable characters and symbols. ANSI is similar to ASCII.
Codes {ASCII code} can use 7, 8, or 9 bits to represent 128 or 256 printable and unprintable characters and symbols.
Memory locations or switches can have two states {binary code}: 0 or 1, on or off, zero voltage or unit voltage.
0 is impulse-pause, 1 is pause-impulse, and start or stop is impulse-impulse {Manchester encoding}. Start-bit impulse interval sets transmission rate, so transmission rates can vary.
Outline of Knowledge Database Home Page
Description of Outline of Knowledge Database
Date Modified: 2022.0225