This article is about the unit of information. Confusion often arises because the words bit and binary digit are used interchangeably. But, within information theory, a bit and a binary digit are fundamentally different digital communication by simon haykin pdf free download of entities. By analogy, a binary digit is like a container, whereas information is the amount of matter in the container.
This usage distinguishes the quantity of information from the form of the state variables used to represent it. When the logical values are not equally probable or when a signal is not conveyed perfectly through a communication system, a binary digit in the representation of the information will convey less than one bit of information. However, the shannon unit terminology is uncommon in practice. Bell Labs memo on 9 January 1947 in which he contracted “binary information digit” to simply “bit”. Bits can be implemented in several forms.
The specific voltages are different for different logic families and variations are permitted to allow for component aging and noise immunity. 0 and 1 at the output of a device are represented by no higher than 0. 4 volts and no lower than 2. TTL inputs are specified to recognize 0. 8 volts or below as 0 and 2. 2 volts or above as 1. In contrast, the upper case letter B is the standard and customary symbol for byte.
Multiple bits may be expressed and represented in several ways. The trend in hardware design converged on the most common implementation of using eight bits per byte, as it is widely used today. Like the byte, the number of bits in a word also varies with the hardware design, and is typically between 8 and 80 bits, or even more in some specialized computers. 0 or 1, up or down, current or not, etc.