Describe absolute binary, BCD, ASCII and Unicode.

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Absolute binary, BCD, ASCII, and Unicode are all different methods of representing characters, numbers and other data in binary format.

1. Absolute binary: Absolute binary is a numerical system that uses only two digits, 0 and 1, to represent all numbers and characters. Each digit represents a power of two, with the rightmost digit representing 2^0, the next digit representing 2^1, and so on.
2. BCD (Binary-Coded Decimal): BCD is a method of representing decimal numbers using binary code. In BCD, each decimal digit is represented by a four-bit binary code, which can be used to represent numbers frim 0 to 9. BCD is commonly used in electronic devices such as calculators and digital clocks.
3. ASCII (American Standard Code for Information Interchange): ASCII is a widely used code that represents characters as a sequence of seven bits. It includes codes for 128 characters, including letters, numbers and symbols. ASCII is commonly used in computer systems, telecommunications and other industries.
4. Unicode: Unicode is a universal character encoding standard that can represent all characters from all writing systems in the world. It uses 8, 16, or 32 bits to represent a character, depending on the complexity of the character. Unicode includes more than 14300 characters from over 150 scripts and symbol sets.

In summary, absolute binary, BCD, ASCII and Unicode are all methods of representing data in binary format, with each system having its own unique advantages and disadvantages. The choice of which system to use will depend on the specific requirements of the application or system being designed.