# Coding-The language hidden behind the computer-reading notes (iii): Numbers

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7. Our 10 numbers

1) numbers are one of the most abstract encodings. Early digital systems: Roman numerals (multiplication very complex)--Ancient Greek digital system (ancient Greeks known for their geometry)--India-Arabic numeral system (today's Arabic numerals)

2) The advantages of Arabic numerals: first, location-related, different positions, the number of representatives are also different, such as 100 and 1000; the second is that 10 and 0 are specialized symbols, of which 0 is the most important invention in the history of mathematics, simplifying the very complex operations in the digital system, especially the multiplication algorithm.

8.10 of alternatives

1) The number can have decimal, octal, binary representation (can be added and subtract between each other, interchange). Binary is only 0, 1, can represent the switch, whether the current is passed, whether the bulb is shiny.

2) The binary is closely related to the computer.

9. Binary number

1) bit (binary digit-bit): The basic unit of information block, bit is the least information transmitted, any content less than 1 bits is not a message at all.

2) general product Code (UPC, commonly known as: bar code, is also a binary code, consisting of 30 vertical stripes of different widths, decoded by 12 digits, below the stripe; it is a 95-bit binary code that contains left guard line, digital, middle guard, digital, right protection line. The first number is the number system character, 0 is the regular UPC, the next five digits are the manufacturer code, the last five bits is the product code, the final number is the modulo check character, used for error checking)

3) Information redundancy: The terminology of communication theory, meaning that there is no need to fully know the whole content, just know the key words can be, but there is a part of the redundancy of the error is still necessary, if the code can be easily changed by the customer then this product coding measures is meaningless.

4) Bits can represent words, pictures, sounds, movies, product codes, film speeds, and so on. What you need to do with a bit of information is to calculate the number of possibilities.

Coding-The language hidden behind the computer-reading notes (iii): Numbers

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